Mallard ducks

We've got a pair of mallard ducks who for the last two weeks have been visiting our front garden 1-3 times a day for food  and water and a sleep. They don't stay, always fly off and come back later/next day. Saturday just gone, the male flew off and left the female and hasn't been seen since but she's still visiting though looking a little lonely.

I was wondering whether it's possible to build her a little shelter out of a plastic tub we have a lying around, so she's not so exposed ect. Would she even use it?