My mom (50F) asked me (19F) today if I could book a week off work near the end of July for my Grandparents' wedding anniversary. A little context, I plan on doing summer courses (that I have been trying to enroll in for a year but they're always full) on Wednesdays and Thursdays. I also work full-time every summer to pay for fall/spring university tuition and to eventually save up for an apartment with my boyfriend (20M). On top of that, his and my 1-year anniversary falls during this week. He is my first "adult" relationship and so far, our relationship is the best I've ever had. He treats me well and respects my family; he's shown up to all their dinners, bought birthday presents for my little cousins, and tries his hardest to help with anything they need.

When my mom heard that I couldn't make it, she became upset with me because she had spent countless hours trying to get the entire family in one place at one time (we have some family in different areas of the country and on different continents). I assumed that, because she was asking me to take an entire week off work, the family would be going on vacation somewhere together, but that was not the case. She plans for the entire family to just... chill at my Grandparents' place (which is a 10 minute WALK from our place) for the week.

I would usually have no problem because I am very close to my Grandparents and love them very much, but I'm currently tight on money and really cannot afford losing an entire week's worth of wages or to skip these classes. I explained to my mom that I am not making excuses to skip. I plan on going to work/school and spend the rest of my free time at my Grandparents' with everyone else. She became upset with me and said that I'm being selfish because it could be the "last time everyone is together before my Grandparents die" (which is an excuse my mom has been using to guilt me into attending things since I was younger than 10). I explained to my mom that if we were travelling somewhere, I would absolutely take the time off work because it would be necessary, but if all she plans to do is hang out at my Grandparents' house, then there is no need and I will visit when I can.

She kept insisting that I am making "nonsensical excuses" and that my reasons weren't good enough, so I added that it was actually my 1-year anniversary with my boyfriend and I would not be able to attend anything else that day. He is already hinting at having special plans for that day, which I don't want to postpone because it sounds like he put in a lot of effort. When I told her this, she became even more upset with me and said "it's only your first relationship! What are the chances you even make it to a year?" This rubbed me the wrong way because my mom always told me how much she loves my boyfriend and that he was basically part of the family by now. I offered to take the Saturday, Sunday and Monday off work and spend those three days with my Grandparents so that I could enjoy my anniversary on Tuesday and go back to school Wednesday and Thursday, but she said it "wasn't good enough" and that I was "leaving my Grandparents alone on their special day." She told me that if I wasn't going to put in the effort, then I shouldn't show up at all. My mom and I rarely argue and have a good relationship most of the time, so I'm scared that this might ruin it, but I also feel like she's being unfair because I have my own responsibilities that she isn't respecting. I am trying to accommodate as best as I can but she really wants me to be there for the full week. My family is very close and they are always my top priority, but I don't see how skipping everything else in my personal life for an entire week is more important than just... hanging out with no real plans. AITA?

TLDR; my mom is upset with me because I won't take time off work for my Grandparents' week-long anniversary that she planned so the whole family could attend because I have work, school, and my own anniversary with my boyfriend. Now, she is refusing to let me attend any days unless I take the ENTIRE week off. AITA?