A little history, I initially got two female zebra finches a few months ago. After about a month I noticed an egg appeared, and there was one new egg every day for about three days before the second finch laid an egg, so that day there were two new eggs. One finch, Marshmallow, was quite a bit bigger, and the other finch, Popper, I assumed was younger because the striped feathers on her tail were still coming in. I'm 99% sure Marshmallow was the one laying the eggs consistently, and Popper only laid maybe one or two. That went on for a couple more days. Then two or three weeks later the eggs started appearing again. Around this time I had to take a trip, and I took the birds to my mom's house for her to watch them. She was reporting back a new egg every day until three or four days in when there were two new eggs. It got up to seven in total before I got back home. But when I brought the birds back to my house, I noticed Popper acting differently. A lot less energetic, a lot quieter, and she would spend a lot of time in the nest during the day, which is unusual for them. At one point Popper was in the nest and Marshmallow was standing on the edge yelling to me. The next morning, I found Popper dead at the bottom of the cage.

Anyway, I ended up getting a new bird because I didn't want Marshmallow to be sad, and she seemed really lonely. So now I have Cinnamon, another female. And it's been about a month since I got her, and for the past few days I've been noticing that she goes in the nest during the day a lot more often than usual. She also makes a very distinct whining sound when she goes in the nest, and it almost sounds like she's hurt. She usually loves taking baths, and will start bathing as soon as I change their water. But I haven't seen her bathing for several days. She's still eating and pooping and I see her on their swing, so that seems okay, but she's definitely acting more lethargic than usual. I'm really scared about losing her the same way I lost Popper. Cinnamon has been spending a lot of time adding material to their nest. It seems like she's getting ready to start laying, or she wants to or is trying to.
Is there a way to keep her from trying to lay eggs, so she doesn't become eggbound? I'm worried about her because like Popper she's a lot smaller than Marshmallow, and her striped tail feathers are also still coming in. Every day I wake up and immediately go check to make sure both birds are still alive, I'm so paranoid the same thing is going to happen again.
Kyle