There's a lot of good quality women's riding kit to be had on eBay. I managed to fit my daughter out last year fairly inexpensively, when she was 12 - looks like a lot of wives/girlfriends/daughters have been persuaded to go pilly, got themselves kitted out and then decided they don't like it after all, and decide to sell up.
Jen, on the other had, asked to go pilly and she's stuck with it
Best buy yet has been a ladies' Furygan jacket, leather rather than textile, for under a tenner including postage.
Only snag seems to be that you might have to look harder for anythingsmaller than a size 8.