By the way it sounds, it would make you very nervous and I think that in itself is a good indicator to probably not do it. If you really do love her daughter and feel weird about doing her mom behind her back, don't do it. Either gently tell the mom you can't do it, or if it won't stop then perhaps you should mention it to your gf, but I wouldn't do that unless it really gets out of hand.
It's a tough opportunity to pass up, but if it doesn't feel right or makes you feel bad, it's not worth the guilt that won't ever really go away if you do it and aren't 100% into it. That will eat at your relationship and probably hurt it in the long run.
And don't tell me you can't edit those photos to blur out the face or something. You've gotta at least let us wild dogs have a peek at them a minor consultation fee for all of our advice! ;) Good luck! Keep us posted!
