Prank gone wrong

The haunting

However after that Grace started to see “Hallucinations” of Ella.
She brushed it off thinking that she just missed her,but after a month she noticed that she wasn’t a hallucination,because one night he was going to sleep and Ella appeared.
Ella walked up to Grace and said “Why didn’t you help me?”
Before Grace could respond she started to have trouble breathing and after a minute of struggling to breathe Ella said “Take this as a warning...next time I won’t let you live.”
After another week Ella appeared but in Grace’s dream.
Ella then said to Grace “They've promised that dreams can come true...But forgot to mention that nightmares are dreams too…”
Grace never woke up...