At first blush it sounds like 'phantom limb' syndrome
When people lose an arm or a leg, sometimes they still think they have it, and go to reach for something, or dream about it.
The same may happen to women who have GRS, she may dream about her former penis, etc.
It has benn posited that 60 to 80% of people who lose a lmb feel a 'phantom sensation:
Sherman, R. A.; Sherman, C. J.; Parker, L. (1984), "Chronic phantom and stump pain among American veterans: Results of a survey", Pain 18: 83–95
Off course GCS isn't quite the same as losing an arm or leg, however in some respects losing / converting something that has been with someone so long could be a causal factor for the dreams you described.