I have a 22-month-old doing the same thing right now! It used to be once in awhile, but it's become once or twice a day in the last two weeks. Her biting is completely random though. If anyone gets within a foot of her, she bites. She bonked her head the other day, so I was giving her a hug and a kiss to make her feel better -- and she bit my neck!
This is something that I would normally term over, but she'll be done in 6 weeks anyway. So, in the meantime, I'm letting her play alone whenever I can't be right beside her. So she's in the playpen (with lots of toys) or sitting at the table while I'm making lunch, if the other kids are in the playroom. Then when the other kids are at the table finishing their craft or snack, I'll let her have the playroom to herself for a bit. She's only allowed to be with the other kids when I'm sitting there playing with her. I just don't see any way around it, unfortunately.
She's a great kid, but I can't have her randomly biting the others
I do know though, if she wasn't done in a few weeks, I would have to term her. I would hate to do it because her parents are great, and she's a perfect kid, except for the biting. But I would have to do what's best for the group.
You've got to figure out if it's worth keeping your biter and doing the shadowing/separating thing, or if it's a better use of your time to let her go.