When we first met I was able to fully penetrate my wife and then she began having problems with vaginal infections and pain during intercourse. For years we attributed it to "female problems". In the first 10 years there were occasions where I reached full depth, but gradually we had less and less sex because she complained about pain during intercourse. For the next 20 years intercourse was very rarely tried and always without success because of pain issues. It is only recently that we figured out that part of the problem was that I am about 7.5" x 6" and that was contributing to the problem. She started dilating her vagina and that has helped. After her hysterectomy her vagina is shorter and that is part of the current problem. We still can't achieve full penetration, we have come close on a few occasions in the last several years but then we quickly are back in the half-way if she is very relaxed and sometimes she will only let the head of my penis in and complains about pain. One interesting note is that she uses a vibrator on her clitoris and while it helps she may also have an orgasm and when her vagina starts to contract there is a lot of pressure on my penis and if she orgasms she can nearly push me out. I believe that part of the problem is psychological because of the years of painful intercourse she expects sex to hurt.
One morning she came into our bed and offered to let me try anal sex with her, she had been dilating her ass as well as her vagina, we carefully had successful anal sex. On some occasions she can fully relax and enjoy full penetration. But in the last 3 months she has not been able to relax enough so that we can enjoy anal sex.
Long story but the point is that there are many facets to a womans sexuality and as a couple you are in a temporary tight spot, patience and understanding are your best bets along with the realization that you are in this relationship for the long haul.