TL;DR at bottom

I’ve (17M) known my GF (17) for about a year and a half and ever since we first started hanging out her mom’s been pretty controlling about how late she’s out with me, frequently complaining about this. Ever since we started dating about 4 months ago, it’s only gotten worse. We frequently have movie marathons at my house but they almost always get cut short by her mom sending her a text like “Be home by 9” on Friday and Saturday nights, saying things like how my GF needs sleep, among other reasons that don’t really add up. My girlfriend obeys her mom without any argument, and I get her home at the specified time, no questions asked, but this has happened for so many dates in a row that I’ve started believing her mom just doesn’t want her spending time with me. 

I didn’t say anything until today after my girlfriend texts me saying she needs to cancel our next movie marathon that we planned days ago because her mom decided today that it’s going to be a family day, which was kinda the straw that broke the camel’s back, per say. I asked her if her mom didn’t like me, I got a kinda flakey answer, which make me go into a bit of a rant about how I felt that her mom didn’t trust me, was making up random things to cut our plans short or interfere with them entirely, and how I felt rather insulted by it. My girlfriend didn’t really say a whole lot other than her mom wouldn’t change so I would have to learn to deal with it and that I can’t take is so personally, at which point I apologized because I realized I was bothering her.

Throughout some more conversation I apologized repeatedly, and my girlfriend said it was fine about 4 times until she finally said that she didn’t like me talking shit about her mother like that, that it really bothered her, and that her ranting about her mom is different because it’s her mom.

We’ve resolved the fight and it led to some very healthy discussion, but I’m still wondering AITA? On one hand I feel like the asshole for basically making my girlfriend choose between what she saw as shitting on her mom or arguing with me, but I don’t feel like I insulted her mom, only that I felt insulted that her mom doesn’t seem to trust or like me. So tell me reddit, AITA?

TL;DR - GF’s mom consistently interferes with my plans with my GF. Today was the straw that broke the camels back, so I told GF I felt insulted by her mom’s lack of trust in me, GF saw this as shitting on her mom. AITA?