Someone with DNA knowledge can correct me if I'm wrong. But I think Haleigh could be ID'd with her dad or moms dna. Kinda makes me think that they need to test to rule out dna ID on evidence.
Mitochondrial DNA passes from mother to child and can be processed fairly quickly.
I imagine they are seeking Crystal in order to try to match the mito DNA to something they may have found.
I don't think this means she is a suspect- I think it means there is something that they can use comparative DNA analysis on.