she was very rude.
but can i say - you were too nice.
she is a pro, but you need to be on the ball (especially in your line of business) and pick up on these things. you need to have an arsenal of ready-replies (a la "bean dip") for when this happens again.
when she first asked you about the house, you should have been upfront with her "Jellyfish, I'm sorry but I won't be able to help you. I am not allowed to give professional advice without charging you". (note that she basically did a bait-n-switch on you).
when she confirmed that *no matter what* they would be using agent B, that was your cue to say "oh, well, I'm sorry but I can't help you" and leave.
...At this point she seems embarrassed and tells me that I should go, she doesn't want to inconvenience me any further. Admittedly, I'm feeling pretty deflated at this point but I tell her that I'm here now and so, I would do what I can to help.
She perks up immediately and happily takes me on a tour of her home and I offer her several pieces of useful advice (which she follows) and give her a price.
see what she did here? she "seemed" embarrassed, plays the game of "you can go, it's ok, don't worry about me", which makes *you* feel bad so you stay and she perks up immediately
sounds *exactly* like a 3YO who cries great big crocodile tears, and when parents give in to her demands, turns off the fireworks and turns on the smile.
next time - just say no. dont' wait for people to treat you professionally - you need to *be* a professional. it's the same with doctors, dentists, lawyers, etc - everyone wants something for nothing...