It took my wife years to have her first orgasm. Oral, digital, penis didn't matter. I just figured she was one of those women that never had them. Then one day she just started having them with PIV and having them pretty frequently. Sometimes gushing orgasms that would leave me soaked. After talking to her it turns out she had got close before. She was getting the have to pee sensation which is supposed to be a sign of impending g spot orgasm. The problem was she was freaked by the sensation and would do things to prevent it from going further. We had almost 10 years of good orgasms.
Then things slowed down to where she rarely has them. Now 90% of the time she cant have one with PIV.
This used to work good for my wife. Try very gentle foreplay. Very light clitoral stimulation. No fingering. If she wants something in her vagina make her crazy hungary for your cock instead. Don't let her orgasm. Get her 90% there. Just before sex have her give you head and some stroking so she gets to feel in her mouth and hand what her vagina is about to get.
Also try this if she doesn't orgasm prior to you cumming. Continue having sex even after you cum. Even if you start loosing your erection. For some reason my wife has her best chances of orgasming nowadays when we do this. I don't know if its my cum or my less than full erect dick that does it but for some reason it occasionally works.