Just because a woman has sex with another woman does not make her a lesbian, most are bi-sexual and women are naturally and psychologically predisposed towards this, as opposed to men.
I must strongly disagree with you. Sex with the same sex is homosexuality/sodomy however you cut it.
Lesbianism is defined by the act. If you engage in a lesbian act, then you are a lesbian.
If you do not engage in lesbian acts, then you are not a lesbian.
It's not really about feelings no matter what you might want. It's about behavior!