So... this is about a girls, girlfriend who ended up with a disease so she went back in time to prevent it? The logic there is kinda empty instead she should want to try to do more with her or they should adopt a child and raise it until she passes
Finally, finally, finally a hero or heroine who, faced with a context that obviously is radically changed, doesn't spend even a single chapter in denial!
She's on a dialysis machine so she probably has acute kidney failure. Idk how she could prevent that unless it was caused by an infection that wasn't properly treated. If its just bad genes, she's pretty fucked.