For starters good on you for being there to support your friend! Ok, I had to use a nipple shield for a while until mine healed..and one of the reasons the baby might not take to that side is because it takes a bit longer for the milk to come out. Baby might also have a favoured side-my ds liked the left better. ...feed feed feed as others have suggested. I think my ds fed for about an hour and a half in the beginning..and stuff the 4 hourly rule...especially if baby needs to gain more weight.
Another idea- If the baby isn't taking more than 5 minutes on the one side have your friend express afterwards..until she doesn't need the shield anymore...
when i didn't need the shield anymore i just took it off..there's no weaning process...just make sure she's putting it on properly...i had LC's and midwives watch me use it improperly without saying a word!!!...it should not just be placed over the nipple (like i'd been doing)..invert the shield, so nipple pointing to nipple, then close the rest of the shield over the areola holding it in place with one hand, then carefully, pull the nipple part of the shield out. it should make a suction and pull out the nipple for better attachment (sorry if that's obvious to anyone else..it wasn't to me).

for you and your friend. hope that helps...if i can think of anything else i'll come back.