Is this her first or possibly her second year teaching? She may not realize that she is wearing her heart on her sleeve. I think it's natural to favor some over others, but as a teacher she needs to treat them all of the same. Could you possibly nicely talk to her about it?
"I know DC can be annoying with asking repeated questions or whatever. We are working with him at home on this. It feels like you don't like him as much as the other kids." See what she says.
Also, parents feel more than kids I think. I always thought that certain kids were being mean to my DS, but he never noticed it.