Well first of all, I think shes cute!

And secondly, I haven't read through everyone elses replies, so I don't know if someone has already posted this or not...but since she is still only 5 months old and her coat is a little thin, I would let it grow out a bit more, and then take her in for a good cut. That will get all the "puppy hair/coat" off and will allow for a new, healthier coat to come in.
My friends Yorkie had really, really THIN hair from being sick with Parvo when she was a baby..and the poor thing was looking pretty sad there for a while

Anyway, I kept telling my friend to take her in and have her groomed so get all that broken puppy hair off - she did and it made ALL the difference in the world! Her hair is so much softer now, and doesn't look so "scruffy"
Good luck!