I know it's weird to think about but if people enjoy sex.. and you want your mom to be happy... I don't see how her having whatever kind of sex she wants to (granted, this would be inappropriate given the context of her being married to my dad) is bad. Of course, not something I would want to see, but yeah I would be glad that she is experiencing something she enjoys if she does indeed enjoy that.
I think you're probably closed minded if you dislike the idea of your parents or anyone having sex if they enjoy it and it's not hurting others.
sparknotes: no it's actually cool if she's into that, come at me