Starry, you haven't stated which GFE services she denies you, but offers others.
There is another possible, but admittedly improbable explanation, suggested by a former SP who is now a platonic friend. She told me that she detested BBBJ but performed it with clients (and not in her personal life) as the agency boss pressured her. Maybe your SP, given the closeness of your relationship calculates that she will not lose you by denying the missing services and/or wants to enjoy sex with you so she does what she likes with you, but provides the missing service(s) with other clients to avoid complaints.
Well I know that her basic service for general consumption is "safe" (which is what I get) but that she is at least amenable to BBBJ. Thing is she almost never offers it to me - I think only twice over 18 months (which I found odd, I mean either you do it or you don't I would think) - other clients I'm not sure whether she offers it more. She does offer DATY to what I guess are her best clients. In my case she was once on top doing her cbj so I was facing the Y and started the action. She repeatedly pressed her groin down on my chest to lock me out. OK. Another time I started to go down on her but she stiffened up like a board and I thought looked pretty uncomfortable so I let up. Eventually I asked her about it and while I did'nt quite understand what she said it was pretty clear that this was not a very welcome initiative. Like I said I could live with it if it just wasnt on the menu but looks like it is for some clients. Its possible that she does it to be accomodating to a good client. I actually inquired discretely of a lucky guy whether she enjoyed it but he did not venture an answer possibly because that was a bit personal and maybe out of respect for the lady IDK. Would have liked to have known tho.