Well, it's not something she really has to learn. She probably already knows this. If she were in a pasture and another more dominanat horse wanted the food she had, it would snake it's head out and threaten to bite her. She'd yield her front away from that horse.
you will be working onthe same principle . if you want her to move away from you (yield), then you have to apply as much pressure as it take to make her want to move away from that pressure. If you want her to yield her shoulders, it would be her nostril that you woiuld focus your pressure toward. you can start by gently pushing with one hand on her jaw and the other on her shoulder. if pushing just causes her to push back, then kind of "pulse" with the pressure. If she moves away, stop pushing.
you just work at this kind of pushing and stopping when she moves. after a bit, you shouldn't need to actually push on her, but only push on the air near her and she will move over.
The same concept is used for the hind, though I would put both hands near her hip. you can apply a sharper pressure by pusing with your finger tips with your hand shaped like claws kind of.