Lots of good recommendations below, I'll add Pegasus in Flight and The Ship Who Sang as my favorite McCaffery novels. Mercedes Lackey you do actually have to be careful with, because some of her books are reeaaaally smutty. I remember them fondly from when I was 12, but you probably don't want to be the uncle who gives them to her, come to think of it.
Wrede's Dealing With Dragons series is incredible, the Circle of Magic series is a good read (https://en.wikipedia.org/wiki/Circle_of_Magic), same with the Alanna series (https://en.wikipedia.org/wiki/The_Song_of_the_Lioness).