Oh! That makes sense, I thought you were saying the RIR had a rose comb. Its the black pullet in topic here, correct? I was having a panic attack there... questioning myself, but doubtful.
I knew I was missing something, my bad.
I do that too, as soon as I can get them grit. IMO, mealworms don't count as "oily" and don't stick to dirt as the chickens run and drop some across the grass, so I love feeding them that.
She sounds too far gone. You would have to break her in an elevated dog crate. Usually, elavating a dog crate on some bricks work. That way you create airflow under her and help her to release her hormones. Being broody for too long can cause several issues. She will probably molt once she is...
How old is the bird? Looks like an australorp to me, color matches, body shape, etc. Seems to have white skin as well, but the photos are not very clear. Looks like a pullet, but depends on age.
If your chickens are 3 months, they can eat a whole mealworm just fine. I know because I do it all the time. They LOVE it. That being said, treats should take up no more than 10% of a chicken's overall diet. Earthworms work as well, but I recommend mealworms. I like to raise my own mealworms...