I did research on endocrinology while in college and one of the topics I wrote papers on was the issue of homosexuality and hormones. There appears to be no real evidence that hormones influence behavior in regards to sexuality except to magnify it. Women who take steroids do not start getting lesbian attraction nor do men who undergo surgury for testicular cancer or prostate cancer (and have to be castrated) start eyes men. Many men with high testosterone levels are homosexual but many men with low testosterone levels are also homosexual -- no connections can be found.
Also, in regards to lesbianism and bi-sexuality I ran across studies on women who became strippers or became members of swinging clubs (in the later category the women were all over 30 and had never even fantisized about homosexuality). It is very common for women who become strippers to start having same-sex affairs (some pairing with females for significant time periods and essentually becomming lesbian in sexual matters as well as life patterns) and as for swingers within around 6 months the subjects tend to at least identify as bi-sexual with a substantial number gravitating to preferring female relations (although none in the study left their husbands and became lesbian one must assume it does happen).
The point in the later examples is that when a woman gets involved in these "alternative or fringe" lifestyles I would rather doubt her hormones or genitic makeup changes.
I had observed that many lesbians I knew were physically somewhat masculine - thick waisted, strong featured. These can be symptoms of Polycystic Ovarian Syndrome, and there have been studies that lesbians do have a higher prevalance of this disorder, which causes insulin resistance and increased production of androgens.
Whether the androgens cause lesbian feelings, or whether the often cruel rejection by men of this body type causes a retreat to lesbianism, I don't know.