I've seen all these studies and they don't look at the bigger picture.
Genes are not fixed - for example, eating GM food can alter your genes. If it is the case that genetics (rather than solely epigenetics) is involved in transexuality, then it will be in the same way as for homosexuality. Studies showing a genetic link are always disproven for the general case, and only seem to be true in some cases - what differentiates those cases from the ones where genetics was not a factor is unknown. It is far, far too early to claim anything like "I was born with it." The evidence is not nearly sufficient. If one was born with it, then I'd suggest it was in the same way that homosexuals are affected by their mothers' hormones, rather than something truly hereditary. Hence it is still alterable, if only by looking at one generation previous.
As for brain structure, it is really malleable and affected almost entirely by epigenetic factors, like nutrition and environment. Hormones are the result of diet and stress-conditions and these affect the development of the brain. There is also some change from how one's brain is used. Brain structure might be different for transsexuals, but this more likely points to dietary deficiency or environmental factors (like pollution) than heredity. Brain structure is intimately tied to hormone levels and is not fixed. There are even studies showing that anti-hair loss medications for men can turn them into transsexuals and even homosexuals by disruption the working of testosterone.
In general these studies never look at the bigger picture. Biology, culture and behaviour are very intimately linked. A perfect and simple example is liberalism. It's been shown that poor nutrition leads to sub-par amygdala development, and it's also been shown that liberals tend to have damaged amygdalae. Sub-developed amygdalae result in worse threat recognition, worse recognition of the "other" and less fear. These biological traits correlate well with the basic tenets of liberalism: more permissive social attitudes, pro-immigration and greater openness to radical change.
A similar link exists for homosexuality and transexuality, I am sure. That it has not been found yet does not mean that it won't be. Regardless, it is far too early to claim that homosexuality and transexuality are not, in some way, changeable, even if only by altering the diet or circumstances of the mother.
I am sure she appreciates your heroic act.