I used a nipple sheild with my first for 4 months! Second only 6 weeks - I have very flat nipples,and the kid had a hard time getting that initial latch. Yes, the sheilds are awkward at first, but what part of nursing isn't, LOL? It takes practice, I always kind of bent the "brim" if the sheild up, sat i over my nipple, and then flipped the brim down, so it would kind-of stick dow like asuction cup....put some lanisoh lanolin under the outer rim to stick it to your boob maybe? We sould sometimes have to latch a couple times to get enough in her mouth, and then just let her go, I never took it off in the middle of a feed, we sued it ever feed for four months, then quit cold turkey, pretty much. it never affected my milk, I had an oversupply, and always had , both times, beginning to end of 9 months of nursing for each baby.
Definitely make sure she is opening wide, I used to tickle her lips with the sheild tip, till she opened really wide like a yawn, and then basically smashed her mouth into my boob, in the beginning, really quick, so she wouldn't close up too quick. We got th ehang of it eventually, but it took 6 weeks or so of learning till we were really confident.
Keep working on it, it i shard to learn, but you can do it!
Jessie