My first comment is that I don't think it's necessary to tell OW's W. If OW wants to deal w/ that and be honest w/ her W, then she needs to do that, it certainly won't help YOUR sitch in any way to go tattling.
Since your W actually had an A w/ another woman, you do actually have a few more issues than normal. However, I don't think it necessarily makes her a lesbian. I know my sister-in-law had a fling w/ another woman at one point and is not a lesbian.
I think it probably has to do w/ the fact that females seem to be more 'emotional' and maybe she was getting fulfilled by this OW in ways she felt she wasn't being fulfilled by you, i.e., emotionally and not necessarily physically.
If you two have started counseling and she says she wants to work your M out, then if that's what you want also, you need to trust that. You can't go into trying to fix your M 1/2 heartedly b/c you're afraid you may get hurt again. If she ends up leaving in the end, that will suck, but you can say you gave your all and have no regrets about that.
Me: 38 H: 35 S4, S5, S10 Bomb 01/07 Wanted D - nothing would change his mind Numerous A's prior to D bomb; EA prior/during D bomb Piecing 04/07 Deployed for a year 05/07 Still Piecing 2010 M 11 yrs 05/10