A lot of women feel that way about kissing - far too intimate. They love to be fucked...but kissing is going too far. They'll try and suck your cock right off your body...but no kissing. You did right by assuring her it's ok. Maybe get in there and help with the kiss? How? Up to you. But, your involvement may help get her past that.
My wife wants to do this with a black guy she knows while I watch but she is hesitant on kissing him since it is such an intimate act. I have told her if it happens I am not going to freak out.
Good for you mom. My mom wondered why I desired her so much. Don't you want younger women? Why would I want to fuck younger women, when I can make love with mu