I want to ask my friend for a ual favor?

She is an RMT that I've been seeing for about 4 years for mages,we are both 50,we talk about current events or anything at all ,anyway I get very turned on by her touch and a few times was very tempted to ask her for masturbation and it has kinda stuck in my mind and I just wondered if there was any proper way to ask an improper question?