>Question: if there is a unmated Queen in the hive will she or hive bees kill my new Queen when she gets out?
Probably BEFORE she gets out...
> Should I look for the unmated Queen?
It's doubtful you can find her.
> How long before thay will eat through the marshmellow?
An hour. Maybe a day.
> I can look for the unmated Q with I get home from work if I need to. First time to do this I just dont know.
The best solution is always a frame of open brood and eggs, not a queen.http://www.bushfarms.com/beespanacea.htm
Not only is it foolproof and doesn't require you to know the state of the hive precisely, it gets you a locally mated queen...