the few times I've got a discount I've never asked but been offered, usually similar practice, a personalised not generic thank you email one even recalling her favourite part of the punt in graphic detail - ding dong!, compliments about myself etc (I'm a sucker for flattery meself
) and discount off my next visit.
the last discount i redeemed a few days ago was offered over 3 months ago £90/hour and she advertises @ £140/hr on AW (oh and the best part was the discount came about from a recommendation posted on ukpunting, she's not on here but the punter mentioned on his visit - TOP LAD
)- called her up and suggested a meet and she was the one who said "i haven't forgotten your discount" ...i was over there in a flash even though it's a ridiculous trek to see her.
if you get on with a regular as james says you can hint with a smile and see, I would expect she wouldn't take it badly and it's not a demand either way so she can offer or refuse
though its something I'd struggle to do myself but that's just me