Totally, totally normal.
Your daughter is at an age where she's starting puberty, which means she's going to have more discharge than she used to. It's normal and healthy and an important part of development.
When discharge comes out, it sits on underwear or pubic hair and dries out a little, making little white or light yellow crusty bits. Different women/girls have different amounts of this stuff, and it changes in texture and quantity throughout menstrual cycles. This is all totally normal and healthy and nothing to worry about.
If you ever notice some really nasty green discharge in your daughter's underwear (like when you get a really bad cold and a sinus infection and your snot goes all weird colors), then THAT is something to worry about, and you should make sure she sees a doctor about it ASAP. But what you're describing sounds just fine.
As you are a single father and are going to be dealing with more and more of these issues, I recommend doing a little reading on what's normal and healthy in a woman's development. Something like "our bodies, ourselves" is a classic. I just finished reading "What's up, Down there?" which was written by an OB and takes a question/answer format. Never hurts to arm yourself with information! Especially because your daughter may someday ask you some hard questions about her body. The least you can do is have a few books around that she can read to help her through these changes.
Good luck! And I'm glad you're keeping an eye on your daughter's health. It is important, after all!