Her impulse control is... questionable.
Yes, he would take responsibility in that way. You're not wrong.
Your knees won't get sore because you get fat. They get sore because you don't exercise properly.
I'll say it again Go on attack mode like the hypnosis librarian
Which one are you talking about? Well, doesn't matter. Either of you, go!
she weighs the same as a 8 year old boy and she's on a diet
Too small and too young to need to worry about a diet. And even if you're concerned (you shouldn't) that you got fat (she didn't) because of some temporary period where you ate too much, going back to your usual habits will take you back to where you used to be anyway.