nipple shield question

My babes is using a nipple shield. I've been trying to ween her but can usually only get her to latch for 1-2 feedings a day. My question is, the LC said the baby gets less with the nipple shield than she would without. She nurses anywhere from 15-30 minutes and takes some little breaks in between. She eats every 2.5-3 hours and has had a few nights of cluster feeding (every hour for 10/15 min) Does she seem to be nursing long enough? We go back to the doctor Monday to check her weight gain so I've just been a little worried waiting for that. She does have a lot of dirty and wet diapers.