I just fed your information into the [Steve Morse's Relationship Calculator][1]Steve Morse's Relationship Calculator in this order:
- parent
- sister
- husband
- daughter
- daughter
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 [1]: http://stevemorse.org/relation/calculator.html