...You need to say something or you will be last on her list.
reviewing expense reports is a huge pain in the ass so even if I'm not busy, I find myself looking for excuses to do something else. Additionally, unless your work has an automatic reminder, she may have just forgotten.
If you don't want to shoot her an email, then maybe pop by her office before lunch and just say something like "Hey, I don't want to be a bother, but I could really use the funds from those Nov / Dec work trips I tool." I can't imagine she would be upset.