So me and my gf recently got into an argument over how she is going to spend her money. So normally every year my gf’s dad, her younger sister (Samantha), her youngest sister (Rachael) and I go on an annual cruise in the summer. Normally, the dad would pay for Samantha’s and Rachael’s cruise tickets since they both do not have real jobs yet and are still in college. My gf and I pay for our own tickets as we each make around 80,000 / year. 

Money must be tight this year, so the dad said that he would only be able to pay for 1 person this year and my gf suggested that she would pay for the other ticket. I told my gf that that is not a good idea, as the cheapest ticket for this cruise is at least $1500 including taxes and fees. My gf is a very thoughtful and compassionate person and who’s always willing to support her family if they need help, whether it’s ordering an Uber for her sister to get to work or helping pay her mom’s rent; I am fine with that and it’s a great quality that I love about her. However, in this case I think it’s a bit silly to pay for someone else’s vacation and I explained to my GF that $1,500 is not chump change. 

She said that she can pay it on her credit card and she can always pay it back. I explained to her that credit cards are not free money and you have to pay it back. Also, she has $24,000 in student debt and I told her she needs to focus on paying that down before she subsidizes her sister’s vacation. I’m also paying her portion of our rent just so that she can pay off her student loans faster.
We also have a 3 week vacation to Korea planned in the fall that we have yet to book hotels for, which will be probably be around $2,000. I’m trying to explain to her that just because you pay for it does not mean you can afford it. And while I understand that this cruise is a family tradition, it’s not life or death situation.

I was trying to suggest alternatives like between now and summer, couldn’t Rachael get a part time job while she’s at college and at least help pay for a portion of the ticket or if Rachael’s Mom could chip in a little bit. I understand that family is supposed to help out family and money is just a tool, but I feel like in this case, my gf shouldn’t be subsidizing her sister’s  vacation. If her sister really wanted to go then she would just get a job on the weekends and at least contribute something.. I don’t want to control how my gf spends her money, but I do want to make it clear to my gf that her idea is a bit silly, especially since she has debts of her own. After our argument my gf won’t talk to me,  accuses me of being cheap, giving me the cold shoulder, etc... AITA?

TLDR: GF wants to pay for an expensive cruise vacation on her sister’s behalf so that they can take an annual family cruise despite her having 24,000 in student loan debt and other expenses. AITA for suggesting that she does not pay 1,500 for her younger sister to come along?