I found no evidence that Stephen King has a Part 2 IT in the works.

I read Stephen King's It, back when it first came out in 1986(yeah, it's a pretty old book), and it's one of my favorites. I was around the same age as your sister. It's one scary book, with a lot of great kid characters. However, I think Pennywise the Clown(creepy dude living under storm drains and bathroom sinks) has been in retirement for several years. Did you know Stephen King has his own Fan Website? Maybe your sister could go on there and find out if Mr. King is planning to write It2. The novel It was made into a movie in 1990, and it's available on DVD. I'd like to see Stephen King write a sequel to It. Great reading!!