When a straight woman is enticed into loving a member of the same sex. Usually through some wild experience or situation.
Angelina Jolie apparently causes the lesbianing of many women. Another is Sienna Guillory. In her breakout role as Jill Valentine in Resident Evil: Apocalypse (2004), she effectively turned a good amount of the straight female population into lesbians.
Can be used to describe homosexual men becoming straight too. The reason why there is no "gaying" or "heterosexualing" is because this phenomenon has mainly occured among women. This is why lesbianing has its cross-use applied to homosexual men becoming male.
"Sienna Guillory is a hot fox. I kept drooling in the theatre while watching Apocalypse" - Former Heterosexual Woman