First off, probably most first-time bunny moms manage to do well enough the first time to be successful... it's just that you get so many threads in which that wasn't the case, and not as many of the ones where nothing went wrong.
The reporting is a little out of whack, is all. But chances are pretty good that she'll do fine.
If she doesn't, and it is the case many times, then I'm afraid Mopsy probably would not be able to take them. There is a chance, but her milk supply is probably dwindling now. Her kits may even already be weaned... but if you are actually seeing her feeding them still, then naturally they're not.
I suppose if she is still feeding them, then you might have a chance if you remove her kits. But your best chance is with their own mother, just because of the stages they are at with their litters.
Keep a good eye out. If you catch her kindling on the wire, you may be able to move her nest to the nest box and she might finish in there. If not, just rescue them as you can and put them in there. If there's no fur, use some of Mopsy's... the smell really isn't that important.
When she's done, check the nest to be sure it is clean and dry and has fur in it, and remove any dead kits or placenta or bloody hay.
If she starts digging in the nest box after she has kindled, remove the nest for a few days, keeping it in a secure place, and taking it out to her morning and night for feeding. (This would be her nesting instincts kicking in a little too late, and you just have to get her past it.)
If she does not feed them within the first 24 hours, there might be a problem. If they haven't been fed in the first 48 hours, there's a good chance she might lose the litter. After 24 hours, you might want to take Mopsy's kits out for a few minutes, and give Mopsy the nest to see if she will feed them. You would need to do this maybe early evening, when she probably has not fed her litter yet (if she's still doing so), but might have a nice amount of milk and feel like nursing. She might be able to give them enough to keep them going until Flopsy's milk comes in.
Good luck! Chances are, everything will be fine, though... just be observant, so if something goes wrong, you can hopefully be there to correct it. It seems to me like kits on the wire is maybe a more common first-time issue than not nursing.
