D. rotundifolia varies a lot depending on where it is from. Plants from colder climates tend to have shorter petioles from those in warmer areas. The alpine plants like those from Grass Lake or Lake Tahoe region are much more compact than those from Big Lagoon, CA.
The leaves on D. nidiformis are curved or bowed so the shape looks different depending on the lighting and angle of view.
This photo illustrates the bowing (pardon the blur)
Taken from this angle the leaf looks like this
Here is another leaf (not as curved) from different angles
These were taken in sunlight. If I used a flash it would have made the leaves appear even flatter and any curvature less obvious. It's because of curvatures like this that naturalists will flatten leave specimens to use for their illustrations.
I took a couple pictures of a recently transplanted D. intermedia "Cuba" that looks younger than Cindy's, but you can see the leaf shape is almost exactly the same.
Here they are compared:
With D. nidiformis, you're be able to see the dip/bowing no matter what the lighting conditions are like because the tentacles lean inwards at the middle. I can't see any bowing in Cindy's pic.
Here is a pic of D. anglica "Hawaii" compared with Cindy's. The pic is from Sundew grow guides.