Kegals do help, but approaching the topic would be near impossible without hurting her feelings. She already is feeling inadequate. The do, however, WORK. Oh they do! When me and my boyfriend first started having sex, I would get so wet and he has a large penis but still it felt to me , like i wasn't providing him with the friction I should be. Even though I thought at first being so wet was the problem I realized there must be something else causing the lack of friction. It was obviously not his penis as its quite endowed.
It through me off, because I had everything so backwards. I hadn't had sex in a very long time before him so I assumed I would be naturally tighter there... Not so. I wasn't exercising those muscles so they weren't conditioned to squeeze on him like they should be.
I started doing kegals at all traffic lights any red light... kegals. The improvement was almost immediate but has bettered over time... now when he enters me I can squeeze him so tight in any position and the sex is so much better for me and I assume for him too.
However if he had told me initially, hey try some kegals, I would have curled into a ball and cried all night. Maybe the ladies here have some suggestions on how you can approach that topic or run into it incidentally that could help spark that idea to do it on her own.
If you can only orgasm behind her, she never gets to look into your eyes as you orgasm and that is a pretty nice moment of intimacy for a lot of women. Like WC suggested , there are positions in missionary that can reproduce the feeling of her being on her stomach, legs over your shoulders or over her head being a few.
That doesn't mean you can't still do it the other way, if its more friction for you on her tummy - trust that its more friction for her as well and probably feels a lot better for her too.
Since she can't see your face like that, your going to have to use words to let her know you are right there with her while you are back there. Like caterpiller suggested, lean in close kiss her neck, bite her shoulder gently, make her feel like its her your having sex with. I think sometimes intimacy is lost in doggy since we can't see you. If your also physically apart during the penetration it could be anything back there... remind her its you.
99% of the time, my boyfriend achieves orgasm easily through oral or any sex position but occasionally (rarely) after a night of heavy drinking or very stressful day ...while pleasing me numerous times , we don't seem to be able to finish him off. I USE TO take it increddibly personal , thinking I didn't excite him enough to make him pop his top.
But after becoming more secure with him in general I never let something like that get to me. I don't orgasm each and every single time we do it, most times yes
sometimes I just can't free my mind enough... and that doesn't make me blame him, and its not anything he is doing wrong... so once I was able to see that guys sometimes experience that too I didn't let it make me feel inadequate.