Alright, Sara. Looks good, but there are a few things.

1 - I'd like a full description of your appearance when shifted as well. This includes size, etc. 
2 - Tied to #1. I suggest a different picture for reference (you're still welcome to have one, but a description is very much appreciated and preferred). I looked through a couple pictures and founds this one that I think fits: [url=http://img4.wikia.nocookie.net/__cb20130619223817/mythology/images/f/ff/Fenrir-2.jpg]http://img4.wikia.nocookie.net/__cb20130619223817/mythology/images/f/ff/Fenrir-2.jpg[/url]. Fenrir is often portrayed as black, so that's part of the reason why I suggest a different reference picture. Also, Fenrir is a - to say the least - very large wolf. Which means that your fully shifted form being abnormally large is actually somewhat expected. I'm not talking eight metres long, but definitely at least twice the size of a normal wolf (think Dire Wolf from Game of Thrones). Possibly, since I read a passage about Fenrir which said "his rapid growth", it's implied that he grows, and will continue to do so until slain. So her fully shifted form getting larger and larger as she gets stronger and more used to it (up to a certain cap) is a suggestion from my side.

3 - She's 18 years old, but she heard about Shifters in 5th grade. Shifters appeared 2 years before the RP begins, so that's when she was 16. That would be in/near the end of her 9th year of school. Please change that bit. 

4 - This is actually a compliment. I like your idea of her having a bit of trouble controlling her Shifting, in that she is "forced" to shift every now and then simply to avoid it happening at random. It's a good idea and I think it would be fun to see in RP.