I've got to shift my Mrs' old Rockhopper SL Pro (15") with Rockshock Reba forks, Juicy brakes (although might swap them for a SLX/Deore combo I've got lying about if you like) and a mix of XT and Deore shifting. 26" though, not great condition but it'll be cheap.
Nominal 'small' should do it I think. She's 5'6".
@howard a bit much for now I think, simple 650b with decent fork or rigid should be fine.