Dirk, I'm not going to rip you apart because the other ladies already did that for me.
Kegel exercises. Though I wouldn't know how you'd approach the subject 'gingerly' that is. Frankly if I had a lover who told me my vagina was too big, I'm sure i'd be offended and most likely lash out somehow in the form of a cold boot under the table and up someone's back side. But you did come here for advice? Google it. Also something called 'NeoControl' or 'magnetic Chair' that stimulates the muscles in question.
Honestly, how the heck would you even bring something like that up? I mean, even if after time passes and you and her meet for coffee to shoot the shyte so to speak, what would say?, "Hey, your great but did you know that for me anyway, your vagina's uh, pretty spacious and uh, I wanted to let you know in case you weren't aware"?? Insert (Slap) or maybe, who knows, maybe she'd laugh. If she's had children and lived a life, I'm sure she's fully aware of her private parts and all they are for her.
You also have to consider this though Dirk, It may be just you. One ought consider that don't you think? Sad part is, this lady may not be getting satisfied; then again, she may be doing just fine.
Anyway, I don't know how you'd approach something like that without seriously hurting feelings. Obviously, it is a touchy subject
but as I said, between a penis pump and some toys, it might help