I actually feel that it is rude to ask for a tip. Tipping is above and beyond. Sounds like she needs to increase her rates.

I visit mainly independents and so instead of tipping I prefer regular visits.

You did not say whether the lady was indy, agency, AMP, or SW.  I also assume you meant in the middle of the session, unless you booked some unique multiple session event.  

I have no experience with SW, so do not know if that is the norm for them.  Being asked for the tip during a session with AMP girl is decidedly bad manners, but does happen if no prior arrangement has been made.  Thankfully, I have never had such a comment from indy or agency.  The more posts I read, the more fortunate I find myself as it relates to ladies I have met.

But to specifically answer your questions - yes, IMHO, it is a mood killer.  Yes, were I to encounter such a question during a session I would not see her again. (Of course that is easy to say when the lil guy is relaxing behind a keyboard, but when he gets some attention from a lovely lady - who knows what the hell he will offer up.)