My grandma had 3 kids. Her daughter Sally is my Aunt. She has a step daughter. Her step daughter has a daughter. My Aunt Sally is her Grandmother. What does that make us?
I just fed your information into the Steve Morse's Relationship Calculator in this order:
and it returned that your parent's sister's husband's daughter's daughter is to you a
??? (non-blood relative)
If you ignore the "husband" that led to the step then you get (as @TomH said)
1st cousin once removed (blood relative)
If you really want a label for the non-blood relationship between you, then I think the following would be as good as any:
step 1st cousins once removed
Well ignoring the "step" aspect you would be first cousins once removed. See How to determine relationship with a cousin? for details of how to calculate cousin relationships.