She hears Sans call out and gives a small nod. He won't be able to see it, but she doesn't want to call back just in case Croc didn't hear. They stand a better chance of getting away if she doesn't give much acknowledgement.

And then the fireball hits.

He's down. Toriel takes a step or two forward, watching carefully for any sign of movement. This could be a feint or it could be a faint, and she wants to be sure before she takes it for granted.

No, he's definitely down now. Miserable creature.

All this magic use is really wearing her down, but she isn't done yet. She lets the firewall fall away and, with another gesture, summons a column of embers to spin gently around Croc's fallen form. It's not much of a prison, but if he wakes up, it should hold him in place for fear of getting burned again. Hopefully, it'll be enough to let him calm down.

Satisfied that this should do the trick for now, she turns to glance back at the two Sans-es, hoping they're alright.