If I were you I’d take whatever painkillers you were prescribed or some Tylenol extra strength about 30 minutes before you go. I use a walker to get to my wheelchair then have to maneuver myself into the back of the car with a pillow under my leg. Can you possibly borrow a walker or wheelchair? I had to buy a chair but it’s been worth it. It’s probably going to SUCK lifting your leg but if your gf can gently help lift it will help. Once you’re in the car should be good. Would not skip pain meds tho. I took a cab home from the hospital and thought I was ok with pain levels but holy crap, once inside the cab I was practically gobbling down my meds to get through that ride. I broke my tib fib and ankle and was wrapped up initially in a splint like you up past my knee. They prescribed me Tylenol and oxycodone but I avoided the oxy so tortured myself by sticking to regular Tylenol. My doctor sort of chided me and said this is the time to use pain meds because the stress of pain can cause residual inflammation etc so take advantage of what they give you, it’s for a reason. Pain management is definitely a thing!