Not sure if mama duck will accept them but she might if you put them where they lay. and as for them being in the frig, people buy Trader Joes fertile eggs and hatch them all the time and they are in the cold where they keep regular eggs at the store. I say give it a shot.
Only way to know is to watch her, does she disappear for a while then you see her again? if so most likely she has a nest somewhere. About her not sitting on them at first, just because they start to lay doesn't mean they will go broody right away, And they like to build a clutch before they do, some will lay 4-5 then go broody some want to lay as many as they can before sitting full time. Just depends on the duck.
If it's a safe place for her to lay and brood then I'd just let her stay there. She'll lay till she is ready to sit. So give her time. are you going to put the refrigerated eggs back into the nest?Just remember is she isn't in a safe place to brood then you run the risk of losing her and her eggs or ducklings if she was to manage to hatch them.
