50% will still work for a lot of roaches. Sounds like the room may be taking away the humidity, especially if you are using a furnace to warm the house.
I'm curious what substrate you use. This is the glass tank with the lid configuration you describe above?
Also what is humidity in the room where the roaches are kept?
Housing them together shouldn't be a problem. They will most likely hiss and one may show some dominance but they are unlikely to hurt each other.
If you can get a couple nymphs they will live longer.
Does the lab house them all separately?
https://roachforum.com/threads/female-dubia-with-vent-issues-possible-prolapse.9821/
Here's something similar. Hope it helps
There are lots of similar posts and I read three or four with all the same advice
She is a hisser, yes?
If so than what she may be doing is "airing out" her ootheca. It is kind of difficult to see in that photo to be honest. Hopefully that's all it is, and it is normal for her to do so once mature and breeding.