There are two ways to approach it, one of which works a lot better than the other if it is someone you like to see and prefer to continue seeing.

One way is to tell her what you want and see if she will do it and for how much. This sounds like it makes perfect sense, but here is how it can go wrong. Her answer will probably depend on how much of the rent she has covered this month, and if the answer is not much, she may agree to do something she really does not like in order to get that extra cash. This can be great, for one date. But if she is good at this job, you may never know whether she likes it or hates it, and if you have a great time you will probably expect, certainly want, to do it again.

All of which leads to a trap where you want to keep seeing her to do X, Y and Z, but she hates Z. And when she finally tells you she hates Z, it may also mean you stop seeing her, for many, many reasons.

So the better approach is to simply ask her if more is available, and then ask her to tell you what else she likes doing. Have her offer other services. Then, whatever she offers you will know it is stuff she is fine doing, and will be happy to keep doing with you as long as the two of you keep meeting.

With pretty much every lady there is something or other she will do with good clients, but does not list publicly for some reason.

And if you do not intend, or want, to keep seeing her much longer, then ask for whatever you want, no worries. She will either say yes or no, and the issue of it being something she hates, but is doing for a little extra $$$s is not going to be a problem for you. But if you want to see her, even if she asks you what you want to do, get her to tell you what the extended menu is, because it works better for the long term.

The ideal is to find a lady you like, who also likes doing what you want to do; the trap is trying to get a lady you like to enjoy what you want to do because that never lasts.

zig

after she got to know you, would allow extras.  She never would set a FS rate but expected a nice tip.  Her FBSM rate was reasonable, about half what I was paying FS gals.  So I added enough to double her basic rate.  It was a lot of pressure on me...  too low & she'd not want to play again.  Of course, she'd never complain of too large a payment.  
My approach would be on the flip...  when you are really into her...   ask if she'd do a BJ or CG?  By then she knows you are safe...  She'll probably agree & let you know the terms.  Good ideas to have a condom with you.  One gal I'm looking at sometimes does but doesn't like to keep condoms there (even asked a gent to take the used one with him)...  so it might happen that way.