Inspirational quote for Sweet Sixteen girl?
She sounds great! Don't know if this is right, but I gave it to my daughter before she left for college and she kept it on her wall. It's from Agatha Christie, of all people:
"I like living. I have sometimes been wildly, despairingly, acutely miserable, racked with sorrow, but through it all I still know quite certainly that just to be alive is a grand thing." That IS great, but I think maybe a little sombre (?) for this birthday... She's usually fairly positive and bubbly, with 'artistic' moods. 
Don't know if this is what you are looking for, but I just did something similar for my granddaughter when she turned 18, I listed all of her broad accomplishments over the last few years and the fine sensitive human qualities she is known for by her friends and family.
This is one of my favorite quotes. It sounds like it might be appropriate for her.
Martha Graham wrote this to her friend, Agnes DeMille
There is a vitality, a life force, a quickening that is translated through you into action and because there is only one of you in all time, this expression is unique. And if you block it, it will never exist through any other medium and will be lost. The world will not have it. It is not your business to determine how good it is nor how valuable it is nor how it compares with other expressions. It is your business to keep it yours clearly and directly, to keep the channel open. You do not even have to believe in yourself or your work. You have to keep open and aware directly to the urges that motivate you. Keep the channel open. No artist is pleased. There is no satisfaction whatever at any time. There is only a queer, divine dissatisfaction, a blessed unrest that keeps us marching and makes us more alive than the others.
Additionally on a different note:
“What counts in life is not the mere fact that we have lived. It is what difference we have made to the lives of others that will determine the significance of the life we lead.”
Nelson Mandela
Oooh, both much closer! Thank you! Not sure how much room I have on the scroll, so it may have to be Mandela.
I'm off to bed. If someone else has ideas in the next few hours or days , I don't need it until Sunday morning.
Many many thanks!
Xxxxx
Nothing comes to mind immediately, so I did a search on "inspiring quotes for teens" and found quite a few sites. This one was quotes for teens written BY teens, and some of them are more thoughtful than I anticipated. http://www.motivateus.com/tquotes.htm
Peggy, thank you. I think one is there.
I'm sitting here crying. There are big stories behind some of those 'thoughts for the day'. I hope their families are proud of their writers.
Yes, I'm sure there are some wild stories there. I noticed the undercurrents in quite a few. I really liked a lot of them. Such courage and optimism in many.
This Mary Oliver poem is a favorite of commencement address speakers. But maybe your niece doesn't need any reminder to seize the day?
The Summer Day
Who made the world?
Who made the swan, and the black bear?
Who made the grasshopper?
This grasshopper, I mean-
the one who has flung herself out of the grass,
the one who is eating sugar out of my hand,
who is moving her jaws back and forth instead of up and down-
who is gazing around with her enormous and complicated eyes.
Now she lifts her pale forearms and thoroughly washes her face.
Now she snaps her wings open, and floats away.
I don't know exactly what a prayer is.
I do know how to pay attention, how to fall down
into the grass, how to kneel down in the grass,
how to be idle and blessed, how to stroll through the fields,
which is what I have been doing all day.
Tell me, what else should I have done?
Doesn't everything die at last, and too soon?
Tell me, what is it you plan to do
with your one wild and precious life?—Mary Oliver
Break that's lovely, too. But I have limited space on the parchment scroll so I think this time I'll stay with a shorter quote, and maybe save yours for IB graduation. 
I'm not sure if the image I've attached will come through, but if you can see it, it's a watercolor painting and quote we gave our daughter for her last birthday. The quote is (Sorry, but I don't know how to format it):
There is freedom waiting for you on the breezes of the sky.
And you ask "What if I fall?"
Oh, but my darling, what if you fly?
E. Hanson
Hmmm, I see that the image uploaded, but I can't figure out how to rotate it to make it vertical - sorry!
Lovely!
This would have been perfect for my sister's daughter, now in her 40s and a mother.
“He has achieved success who has lived well, laughed often, and loved much; // Who has enjoyed the trust of pure women, the respect of intelligent men and the love of little children; // Who has filled his niche and accomplished his task; // Who has never lacked appreciation of Earth's beauty or failed to express it; // Who has left the world better than he found it, // Whether an improved poppy, a perfect poem, or a rescued soul; // Who has always looked for the best in others and given them the best he had; // Whose life was an inspiration; Whose memory a benediction.”
... Or the short version: “Live well, Laugh often, Love much.”
--Bessie Anderson Stanley (her poem "Success")
Oh you sweet talker: our family name (and therefore hers) means Unicorn!
Nice! (You might love my collection of unicorn statues, books, works of art.)
joanne said:
Oh you sweet talker: our family name (and therefore hers) means Unicorn!
They have a huge collection as well! In fact, when they moved house two weeks ago, I got a huge unicorn's head from them. 
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Good morning everyone! Happy Valentines, and happy A's birthday!
I went through all the suggestions with D and he read his to me, and this is what he decided we'd use: (I transcribed, and corrected grammar)
Yeah, it's a little preachy, but there was an amazing meet-the-teachers last week, and she's probably going to be asked to take a leadership role in her NEW school that she's been at a whole 2weeks. Remembering to safeguard her resources and her sense of reality, remembering courtesy is probably not a bad thing
Thank you for pointing us to the site! We've noted it for other needed quotes, too
I loved another quote from that site: "You are not a drop in the ocean. You are an ocean in a drop."
Audrey Hepburn have some great quotes. Here are some more on Pinterest.
https://www.pinterest.com/search/pins/?q=quotes%20for%20teen%20girls&rs=typed&0=quotes%20for%20teen%20girls%7Ctyped
Niece's birthday on Sunday. Have gift, card, wrapping paper. Also have 'wish scroll to grow on', but have no idea what to write on it... Creativity has been burnt out by this week's records Audit and weeks of migraines.
She's arty, bright, theatrical, looking (at this stage) for a career in life sciences, wants to live for a while in Italy... Has a thing for modern antique-y stuff (possibly Art Deco or Art Nouveau but she wouldn't know those periods yet), sings well (40/50s harmonies and modern songs), acts, dances, has done circus sports...