A crying corner is for just that - for the child that cries to get what they want, when parents leave whatever. They go there, get it out of their system and then join the play again. I would be setting up the playpen in the playroom right near the play. Then do the swoop and No as Judy said and put her in there - no blanket, toys anything in there but the pad itself. Totally ignore her and start doing something even if it is just sing a song with the offended child and whoever is closest. After a few minutes lift her up so you are face to face and tell her that hitting hurts and we do not hit at (insert your name here) house. Then put her down to play in an area that encourages alone play. Let her progress to the group at her pace and play as she wants till she hits again then repeat. After a bit you will start to get good at getting to her as soon as you see her sizing up her victim and can interject verbally a no (name of child) or it will be back into the playpen. Also take note of anything that is setting her off and you might be surprised - another child, a particular toy, only when a certain sound is playing (such as another child pushing the siren on the firetruck toy) or whatever.

Try to find out if the parents use spanking for discipline. Not that all kids that are spanked become hitters but some do. Hitting at this age isn't really a learned behaviour as much as it is an instinctive behaviour. They act before they think which is why they can apologize and know it is wrong but can not stop themselves from doing it again. Just stay vigilent till she matures a bit more, gets more language. Just because she seems very advanced remember she is still onlyi16 months old.