SD still believes in Santa. The other say when it was just DH, SD, and me DH asked her if she believed in Santa. She said she did and was really confused as to why DH would ask.
Later on DH asked me if I thought he should tell her the truth or not. I'm torn. DS will be 11 next month, he stopped believing last year. With SD's delays its quite likely that she'll continue to believe for a long time, or until kids at school talk about it.
DH wants to tell her the truth. I just don't know.
Also, in case this matters, DH is CP. BM isn't super involved. She has EOWE, but gives up about 80-90% of her visits to either us or BM's mom. BM spends about 12-16 hours a month with SD (time spent in the car driving too and from BM's mom's house).