Is mom hen "clucking?" Mom hens tend to continuously "talk" to their babies by emitting a low, semi quiet "cluck cluck cluck" to them. If she's not clucking to them, that may be a bad sign. Like the others have said, try putting mom and babies back together. If she tries to call them over for food or clucks at them, she's most likely fine and will continue to care for them. If she doesn't and instead just paces back and forth, trying to get away and acts aggressively toward the chicks, remove them immediately. You're going to be mom then!
In regard to her behavior: broodies are stubborn. The nest she picked is the nest she is going to sit in. There are no substitutes. I'm surprised you got her to sit somewhere else. Sometimes broodies will acclimate to a new nest but for the most part, they want their original. She probably, for whatever reason, stopped recognizing the chicks as hers; the same process that goes on in a "homicidal broodies" head. They think the chicks are there to hurt their eggs... bizarre, I know, so she just went back to her nest to sit on her eggs. Or she could have just been confused, thinking her babies were under her when they were crying for help (I've seen it happen with mom hens) and then when you removed them to warm them, the peeping stopped. In her head, babies are dead. Time to make more. Back to the nest. HER nest.
I do all my incubation and hatching through broodies and I've seen a lot of things... and they still continue to surprise me with weird stuff. The main thing to remember is this: every broody is different! Each one raises babies differently (just like all species of moms!). So getting to know each individual mom hen is of utmost importance in catering to broodies.
If she doesn't accept her chicks back and you don't want her sitting on a new clutch, make a broody bin and stick her in there. It is going to take a long time to break her most likely so be patient.
Making a broody bin: a broody bin is nothing more than a cage of some sort with no substrate and a wire bottom. Making sure air passes through the bottom is the most important. I use a wire dog kennel with 1/4" hardware cloth spread across the bottom, elevated 1 foot off the ground so a nice draft comes up through the bottom. The objective is to make it uncomfortable and cool to sit on anything. Make sure food and water containers are firmly attached to the cage because she will knock them over first chance she gets from all the pacing she will be doing trying to get back to the nest!! Most people say to leave her in there until she lays an egg. I find that timeline to not be as concrete as most people say it is. I leave the broody in as long as she is "broody clucking." As soon as she appears to stop and starts making "regular" chicken noises, I leave her in for a couple more days. Then let her out. I always keep my broody bins in the coop so reintroduction is not difficult. I would guess your hen will be in the broody bin for at least two weeks.