To share my two cents, while I don't agree with the total condemnation happening in the thread here as a cannabis user myself, here is how I see it:
OP, I think it would've been best to send a quick text to ask "Do you mind if I smoke a quick joint while I wait?" Then you could get her answer just to make sure she's okay with it and is aware you'll likely smell and taste like pot when you walk in. I also think it may be wise to start carrying a small pack of breath mints with you just in case there is no mouthwash available. Not every SP has some at their incall.
My anti-anxiety meds, being SSRIs, can make it difficult for me to climax and basically edge me unwillingly. Cannabis helps to increase my sensitivity and make it easier for me to counteract the side effects of my meds and reach climax. With that said, I always ask the SP regardless of what their ad does or doesn't say and explain why I'd like to use it. I also don't get absolutely ripped, just enough of a buzz, so I'm still coherent, cognitive, and engaged in the session. I also pop a couple breath mints and/or use mouthwash if available. I also use a weed vape/pen so the smell never gets on my clothes. I have never once had a problem with my way of approaching it.
However, while I think there were assumptions made on your part OP, I also don't think that you should've had a completely bad session as a result. I could understand if she didn't want to kiss as a result. I could also understand her politely turning you away at the door. But to see you anyways, take your money, and give you a lackluster session if the cannabis was a problem imho isn't cool.
I saw Xina a few years ago for a quick visit and had a good time. So I have nothing against her at all and if I were in PK more often, I would see her again.