I don’t know what to do about my MIL… need advice

Sorry this will be abit long. I am 26 and my husband is 29. When we started dating it was nice being around his mom she was very helpful and supportive. Now a year and half into the marriage I’m starting to hate this marriage. My husband is a big mamas boy, he brings his mom into all the decisions even though I asked him not to. We planned a family vacation that supposed to be next weekend. I’m still in school and some of my exams are one on one with an examiner, not written exams. I have been waiting on this big test for months and they know that. My MIL planned the whole vacation. My instructor told me he can get me a spot to take the test soon but it will be 1 or 2 days after the vacation starts. I asked them if they are ok with me flying to the destination on day 2 of the vacation after my test as the airport is near my testing place and parking is not expensive. So they could drive my stuff down with them and immediately after my text I’d catch a plane to the destination. She called me telling me the she has been planning this for months and if I don’t with them on the day they plan to leave that I’ll ruin the whole vacation. I told her it’s not a big deal if I fly down a day or two later and she knows I have been preparing for my test for months. There is a shortage in examiners so if you get a day you take it. She told me that she knows my exam is important but I should prioritize this vacation and the family and if I fly out later that will let her know how feel about them. I have a bachelors degree that I can’t use because of this one exam. I have been doing odd jobs just to pay my bills and loans and it’s exhausting. Some times I work till 4 am driving people around and sometimes I don’t feel safe. She refuses to understand.She basically told me I either choose the exam or the family. At this point I don’t even want to go on that vacation coz starting my career is important to me. My husband agrees with her. Please advice .

Edit: The vacation was planned earlier and the test is on the basis of examiner availability since most of the examiners have regular jobs. It happens that this is when the examiner is available and very hard to schedule the exam ahead of time. Sometimes they can schedule you early and when someone cancels their exams you can have like 2 days notice. Another thing, the state where we live has few jobs in my field and they pay half of what other places are paying. I asked my SO not to take a new job because we might have to move so that we both can get good jobs. He took a new job anyway. It pays the same as his old job and it’s in the same field. The same job he’s doing pays way more in other states. I told him that if I get a job somewhere else I’ll have to move then he can move later. He did not like that. MIL did not like that say it’s unfair to his son and that I don’t care about them. FIL very understanding of my reasons. She has another daughter in law who I was told was a bitch but now I understand why they think of her that way. When I met her there was nothing wrong with her, I talk to her sometimes and I like her she’s a good person just have strong boundaries. Everytime I try to put up boundaries it doesn’t work out well coz my so knows nothing about boundaries.

I don’t know what to do about my MIL… need advice