I teach beginners - little kids. Yeah, sometimes they get mad at me, "I don't like sitting like this." or "This is too hard." or "Why do I have to put up all my own tack?"
Like Jubilee said, the relationship between a teacher and student is different, and professional. She may think that you're just being bossy, or that you think you're better than she is, and that's not good for a friendship.
However, if you still plan on teaching her, I ALWAYS start my students on the ground. They need to know all the equipment, the parts of the horse, how to walk and behave around a horse, how to lead, how to groom, and how to tack up. THEN they can get in the saddle. My kiddos know how to do everything by themselves before they can ride - that way I don't have to babysit them at the barn. I feel comfortable cleaning stalls or getting feed ready while they groom and tack up, because I know they know how.
Depending on the age of your friend, she's probably going to think she can just jump on and start running - all my students think that. She might get mad at you when you tell her she needs to MASTER her seat, legs, cues, turns, stops, and back ups at the WALK before she ever thinks about trotting, let alone anything faster. My students always pout when I tell them that. But it's important.
I hope this has been helpful. If you decide to teach her anyway, you can PM me anytime for tips on working with beginners. I don't teach anything past the trot; I pass them on to a different instructor for that. I just lay a good solid foundation of riding for them.