Allison,
I've read bad things about that shot he wants to give her for her gums or teeth. Be sure to do your research before you let him give it to her.
I think it sounds like a new vet is in order. I don't think I've spent $200 to date on both my girls! That's ridiculous. (of course I know prices vary from place to place) but for a healthy dog...
Take care and don't let this vet take advantage of you and put your Lexi through needless testing and meds.
Just my two cents worth,
Tammy