So, I don't think Van Pelt is Red John but I definitely think she is close to him or is an accomplice. Look at these quotes from various episodes

"The Red Barn": Regarding Visulaize..Grace: What's wrong with wanting to be the most powerful version of you you can be?

"The Crimson Ticket": Teresa: Women can strangle people.

Grace: Believe me I know I could.

"Ring Around The Rosie: To Linda Tibbs "Grace: If you quit now, you're going to miss the best part. Payback.

So she has always had family issues. During the time that Red John started she would be probably 4-6 or somewhere in there. Who's to say that she wasn't having a rough go of it when she was a kid. She needed people to be her "family" and eventually takes her battered and broken self to a Visualize type group and became a member. I know she sits all day because the actress playing her is/was pregnant. But she is one of the only ones who basically watches the incoming/outgoing workings of the group. She could easily put a head up to RJ or anyone connected. It might explain how he is always one step ahead. I just find her recent reactions strange. She is more of a fringe character these days and has a very "bad" girl side to her.

Side Note: This part is out there so don't judge it along with the above paragraph but we don't know where the smiley face on the barn came from. Our assumption is that Red John got his start doing that after he killed those 2 Visualize members. What if it was just some kids who wanted to paint the barn and RJ then copied it as his symbol. What if it was just a Visialize symbol in the early days? Who knows who would have come up with it.