Hard to tell if she's underweight.

The first picture makes it look like she is a little, but not so clear from the other ones.

I forgot from the other thread how much she weighs.

My adult male corn, Figment, is about 640G and eats a jumbo/ex-breeder mouse (35-45G) every two weeks. He's 5 and maintaining weight well on this regime.

How often are you feeding?

If she weighs anything close to Figment, and I think I recall she weighs more, and you want to add some weight to her, feed every 7 days at least a 35-45G mouse, or two 15-20G mice.

Corns will almost always take two rodents, especially if they aren't huge meals (each one).

Some people offer rats to larger corns. I tried a weaned rat for Figment once and he was going into shed (which normally doesn't stop him) and he showed no interest.

In general, corns eat mice. If you want to supplement with a rat every now and then, that would be fine, but I both feed and suggest a staple of mice.

I do not feed adults large meals either. Corns and can eat food almost 50% wider than their body. However, as adults, I leave a small lump every 10-14 days. If you want to bulk her up, feed more often, not bigger meals per se.

Anyway, keep us in the loop, and if possible, answer the questions on weight and feeding schedule if you can. I would be weighing her after a couple of poops and before the next meal (as dry as possible) and see if she's gaining weight and how fast.