Mom too involved in my love life

I'm senior in highschool and my girlfriend and I have been going out for around seven months now. We're happy together, the issue isn't between my girlfriend and I.

Now, for the past six months, my mother hadn't really involved herself in my relationship. Just recently has she been talking to my gf. She's been wanting to take my gf out to get mani/petti's. She's been going over to her house to just chat. She even looked up my gf's number on information so she could talk to her on the phone (and just today, no one picked up my gf's home phone, so my mom left a message cussing on the answering machine).

My girlfriend is 17; my mom is 53. I find it weird that my mom is doing this. So does my gf and her family.

Just a little background, my mom's been divorced for about 5 years now (getting out of a 26 year married relationship). She's also had two diagnosed strokes within the past 10 years (the doctors say she could've a few smaller ones as well;she wasn't like this before her strokes). It's hard to reason with her because she believes she's right all the time and doesn't understand logic all that well. We also just recently moved, so she doesn't have too many friends here.

The answer's not to break off the relationship with my mom, I need a way to get her to stop acting this way towards my gf because it's really starting to bother people, my gf, her family, and myself included.