I suggest taking a look on the main re-enacting forums in the two female sections... plenty of pics of nurses uniforms and ATS. And yes there are loads about. Original and repro...
I've personally just finished getting a KD ATS 14th Army uniform sorted for my other half. That's all original though (apart from the insignia)
As yith says, recommend talking to Katie aka Miss spitfire on the wwii reenacting forum, lots of knowledge and its one of her impressions (brit nurse that is) as well as being well researched (tell her dink told you pm her if you venture on there).
Shame she's not doing yank nurse saw a full uniform for £40 on american ebay for an ARC nurse headress, apron, the whole shebang. Brit bits come up on ebay but its wise to have an idea of whats accurate and whats not (hence talking to kate). Also look for Della Rebous (spelt wrong sorry) or similar on that forum, she makes custom uniforms to fit (all forces), pricey I believe but worth it. Depending on size you may also want to visit places such as malvern (stoneleigh in feb) where you may pick up an original for her 
Sorry can't be more, I research DRK nurses so Brit ain't my forte atm
