Found: YA? Thriller about a mother and her children at the old family cabin, gets haunted by little girl.

Hi there! I'm trying to find a book that I read when I was in middle school, I remember it was fiction. The plot was about a mother, who was a struggling artist, taking her two preteen children to the old summer cabin. I remember there was a lake next to the cabin with a dock and some strange things start to happen. The young girls end up getting haunted by the mother's childhood friend that passed away, she was called 'Sissy' (I don't know why that stuck with me and not the title of the book) I first thought it was "Wait Til Helen Comes" by Mary Downing Hahn, but that wasn't it. I just want to read it again after so long of wondering what it was. Thank you so much for any tips\help!!

Deep and Dark and Dangerous by Mary Downing Hahn.

>2 MissSquish: Thank you so much for the help! I can't wait to read it again!