I think the case was closed because everyone assumed Imli is dead, so for the case to be opened, they need to prove she's alive. So either a DNA test or matching her fingerprints to police records (she was in jail before). Only then will the case be reopened.
My guess is Imli will return in disguise, later on, if they keep the character, she'll be associated with someone powerful and assume a new identity, it's easier than intimidating witnesses and destroying police records.
That's why they made everyone think she's dead because otherwise there will be an arrest warrant against her and the onus will be on her to prove she isn't Imli, now it's the other way round.