Awesome idea here as this has absolutely nothing to do with your friendship with your friend but more to do with the friendship you've developed between her Mom and you so -  yes most definitely go visit her out of that friendship. 

I think that's a great idea especially if you were close to your ex girlfriends mother, I'm sure she would appreciate your thoughtfulness.:)

We'e you and your gf's mom close? If so yes go see her.  It's a very nice thought for you wanting to see her.  I'd go either way!!!

I don't see why not ! It was nine months ago so she shouldn't be upset if you visit her Mom. If her Mom is OK with it, then go see her. Nothing wrong with showing respect and kindness to your elders. I think it's a good idea !