Genuine question: does she have a hyper-religious childhood history and /or abusive background?

She may be having sex dreams while genuinely not realizing what she's doing — both of you feel correct, but her childhood trauma naturally creates this absolute WALL between her subconscious mind and conscious actions, that won't allow her to accept what she's doing. By the time she's awake enough to talk, she's absolutely forgotten the dream.

If curious:

This is how some forms of PTSD present; while nightmares are usually just whimpering and heavily shuffling — don't think Hollywood, think "rigidity of sleep paralysis but some muscles work, then all of a sudden you gasp and open your eyes" — certain unconscious physical actions can become faster or slower based on the pace of the memory/dream. If someone hurt her in the past, she might be pushing someone away and then running — but since dreams aren't long-form memories, the dream ends, her "fists" relax, her fingers gradually unclench and end up in some highly sensitive zones, and that unconscious placement induces a pleasant sex dream a few hours later. This could very easily look like masturbating if you're not aware of historical trauma because she doesn't want to burden you with that knowledge. In addition, unexpected contact [again, based on trauma memories and body location of trauma] to certain sites can induce both a much more violent response ^((please see below)) and a much gentler one. But by the time she's conscious, she absolutely doesn't remember the movements (like people sleep talking), and may have absolutely forgotten the dream, or just remembers a terrible feeling of fear and being trapped. Now she becomes angry at YOU for making something up, waking her up, etc.

Regarding the physical contact thing: My wife is great at stopping my surgery-based nightmare, because I'll subconsciously smell her, feel her hair on my shoulder, etc., and that'll somehow orient my brain so my dream goes "oh, yeah, that's over, isn't it?". Then one time she tried waking me by wrapping her arm around my lower stomach to pull me close (instead of upper arm as usual), and her hand touched my surgical scars. I reflexively elbowed her... 18 months after we had just paid $32,000 for a sinusplasty/nose job combo, to fix a lifelong breathing issue. ^(I still hate myself for that). So your physical contact may have genuinely made her dreams so much better she slept well... Then slept better.

Just another perspective to consider, especially if the relationship has ZERO other red flags.