Do Zebra finches need a nest?

I have two finches, a male zebra and a female society. I was told originally (and they both looked like it) that they were males, so I didn't bother with nesting materials after they didn't seem interested. Unfortunately the society was a female and now has eggs. I haven't candled them yet, but they are laying on the bottom of the nesting container. Should I try to build a nest for them, or would that turn the mother off? If I give them nesting materials they will build it on top of the eggs... Not sure what to do here, thanks for any help.