Sick pregnant guppy?

Hi,
We’re very new to fish keeping and bought some guppies a few days ago. as one of the guppies seemed like she may be ready to give birth (squarish belly, staying in one spot) and the males kept nipping at her we put her in a breeder box. When we checked on her we saw a piece if white fuzzy thing at the bottom of the breeder box. (pictured)
What could this be? Fungi? Pretty sure it didn’t come off her… could it have come out of her?
How do we treat it?

What white stuff?
If you are referring to the white thing at the top right of the picture, it could be fish poop.

Is it normal for fish poop to look like that? We thought it was poop but it also seemed really large for a tiny fish..
Took it out with a tweezer and it looked like mucus

White poop is usually an indication of an internal problem. If the fish is eating well, it probably has intestinal worms. The following link has more information on stringy white poop.