AITA for telling my girlfriend that we are not living together if she wants to split joint expenses proportional to income?

I (28M) met my GF two years ago. My GF is in grad school and lives off of the small stipend she receives and student loans. I make fairly good money.

My GF wants to move in with me. I live in a house owned by my grandparents and do not pay rent (at their insistence). My GF’s current rent alone takes up almost her entire stipend each month. Plus she has a utilities, food, medical insurance, car insurance, car payment, medical bills, credit card debt, etc. The landlord is raising rent and she has not been able to find a cheaper place that feels moderately safe and sizable enough for her and her dog. So, she wants to move in with me.

I currently have a close friend who also lives here. He pays all the utilities as his rent. My GF wants him to move out if she moves in, which he is fine with doing. I have talked to my GF and stated that if she moves in, we should split the joint bills and expenses 50/50. She is greatly opposed to doing that and thinks it should be proportional. That would result in me paying virtually all the joint expenses. A 50/50 split would result in a significantly better financial situation for her. Right now, her living expenses are exponentially higher than her stipend. With this 50/50 split, they would be significantly less than her stipend. I would actually be paying more than I do now with a 50/50 split because I do not pay any utilities right now.

I told her if she insists on a proportional split, then we cannot live together. She is pissed and says I am causing her unnecessary stress. We both can afford the proportional split so that is what we should do.

AITA?

Clarification

It seems a lot of assumptions are being made in the comments, so I need to clarify some things.

Yes, I do love my girlfriend, but I have significant disagreements with her on money. Our biggest fights have been about money. Every summer, she takes a trip somewhere and puts it on a credit card. Last year, she bought a new car. She has a $700/month car payment that her mom has to help her out with. We have talked about these things. She gets defensive and tells me that I have no say over her money.

I am all about saving. I own a small contracting/construction company with a buddy. We started it not long before I met my GF. In fact, met her because I was doing some renovation work in her apartment complex. Basically, we are pinching pennies for the next couple of years to build up our nest egg and hire a staple of people. So, every dollar counts.

If we were truly pooling our resources together, I would be ok wIth proportional. But, that is not what we are doing. My GF wants me to still have no say over how she spends money while doing a proportional expense setup. That is a problem for me.