My Daughter is 5' and weighs 88#. I just bought her a Small (size 6) Ladies Teknic Sequoia Textile jacket. It's a little big on her, but looks pretty good! She is actually going to use it on the motard track when we go this summer. I got it for $129.00. She loves it.

I got her textile so she can use it on the ice in the winter. Oh, and my daughter is only 10 so she is a stick.
As far as helmet goes, I know that Arai measures up to 54 cm for XS. (I am at 54cm and wear an xs) I am sure an XS Arai would most likely work for her. You will need to know what shape her head is though. If she has more of an oval shape, the Arai Signet is awesome (that's what I wear). Otherwise the Quantum is for normal round heads. I had a tough time finding a helmet to fit properly because of the shape of my head. The Arai Signet is the only one that fit perfect. Although, I do wear a Shoei dirt helmet and it REALLY nice. I plan to investigate their street helmets when I am due for a new one. My Shoei Dirt helmet is also XS.
I hope some of this helps. But you will need to have her try on helmets. Verify pressure points and what not. Hopefully she won't be as difficult to fit as I was.