It's very good to give her a whole room!
Very important: what humidity level are you trying to reach? And, what is the humidity reading right now?
If the room does need higher levels then I have a long response to your post.
First, look up the meaning of the term "Relative humidity".
You might simply need a better humidity measuring device. Does the humidifier have a humidistat, which automatically measures the humidity and turns the machine on and off as needed? It may not be working right and needs replacement.
Don't use the ones you get from reptile supply stores. When you look them up online don't look at "humidistats" as they do the job of switching the humidifier on and off.
Your whole house humuidifier is designed to work at normal room temperature, 70 degrees F. When the temperature is raised to 85 F., the air in one room can absorb more water than even a whole house at 70F. If so, then the humidity in the one room will read low and the humidifier isn't productive enough to keep up.
But there is one thing you can do to try to raise it: Stop the leaks. Bedroom doors are commonly installed in a way that lets a lot of air leak in and out. Air leaks dilute room air. Use foam tape around the door and a threshold to seal the door better. It's a cheap fix, and your hardware store people can easily help you.
The other thing is leaky windows. Windows over 20 years old often leak a lot. Newer ones leak less. If you are motivated enough you can block the windows from the inside with clear acrylic (Plexiglass). Shop the prices because acrylic prices vary a lot.
There is a soft, water-clear plastic fabric that would work if you can find it. Staple it to the wall around the window(s) and cap the edges with a 1X2 strip of wood on all four sides.
Doing those two things might fix the problem. If the room's humidity stays low, then the laws of physics dictate that you need to add another humidifier of some kind. The humidity the humidifier puts out may be close to the amount the room needs, so experimenting with an added smaller humidifier may fix the problem. If you add a cool mist humidifier, it should be mounted high on a wall so the droplets can evaporate as the fall.
I hope it all works out.