Look, I don't know if there's a mod for this, but it would be great to have an option during sex where our girlfriend could masturbate. That would be really good.
Please, this is not a place for a mod suggestion.
And also, the mod that you are suggesting is currently impossible to mod.
A proper place for this suggestion should be on the #🔨mod-development channel on the Official MDRG Discord Server.
But please keep your expectations realistic; no one will be willing to create this mod simply because it is impossible to implement.