I'm looking for the name of an older movie about a girl in a dark blue velvet dress who was killed I think by her father and buried in the garden.. I think her name is sarah and she haunts the girl dating her boyfriend I know it has shannon dortzy in it.

There were no hits at all on a Shannon Dortzy, so if you mean Shannen Doherty,
There's a link to most of the movies she has been in at the link below:

Shannen Doherty Filmography

From your description, it may be: Friends 'til the End Synopsis

Sounds like Buried Secrets (1996) (TV) with Tiffani Thiessen.