My girlfriend dislikes my mother

I'm 38 and my girlfriend is 40, we are great but there's a big problem.......and the problems seems to be my mother according to my girlfriend

My mother is 59 years old, and I'm an only child. My mom's been here in Canada 25 years but all her family lives in Dominican

My dad walked out on alll of us when I was young.

I try to help my mom as much as I can. Sometimes she needs a ride to the grocery store, soo I take her.

She had her doctors appointments, I obviously take her.

So last night my mom called me if I could pick her up at 7pm at night. She went grocery shopping in the blizzard and her taxi never came. I drove her home and my girlfriend flipped on me.

My girlfriend told me I'm too old to be hanging out with my mom, she tells me my mom needs to fend for herself, my girlfriend tells me she moved out of her mom's house at 14 blah blah blah

My mother doesn't need me everyday, this isn't an everyday thing. Maybe once a month or once in a blue moon. This bothers my girlfriend and tells me to grow a pair of balls. She called me a mommy's boy and I was pissed off.

Why does my girlfriend have to be this way???

Am I really doing something wrong here