According to this article, scientists have now successfully transplanted ovarian tissue from one non-identical twin sister to the other, who started menstruating normally. If she gets pregnant, she will get pregnant with her sister's eggs - but they will have been matured and released within her own body. So she is only a tiny sliver of a distance away from being the "real" mother. The genetics don't come from her, but they are stored, matured and released in her body. The game of chance (regarding which egg will develop and be released) is played out within her belly.
Then there is the case of identical twins, which have apparently also successfully undergone ovarian tissue transplant-donations.
What about the resulting children? Who is the "real" mother?
Even as I maintain that the "real" mother is clearly the biological mother, the woman who originally produced the eggs and whose genetics are in the children, this twisting of nature is still enough to produce a massive migrane.