Nope.

And, more than likely, they voted for the elected officials that put such a system in place anyway. So they helped create the climate of lax enforcement that cost this girl her life.

Probably not. This would be similar to the lawsuit brought by Kate Steinle's family in California, and a federal judge held that the California law that barred telling ICE when a prisoner will be released unless ICE has a warrant was not contrary to federal law. (Side note: Steinle's killer may well have been released as a result of a mistake by federal officials, not state law.) Local jurisdictions are not required to enforce federal immigration law, anymore than they are required to enforce federal tax law. Furthermore, local authorities can themselves be sued if they detain someone beyond their state-law release date without a warrant.

If the PG County officials were following state policy, they likely cannot be sued.

https://m.washingtontimes.com/news/2019/may/22/joel-ernesto-escobar-illegal-immigrant-murder-susp/

The politics of ice detainees aside, can the murder victims family sue PG County?
Common sense tells me yes, but I assume the bureaucracy has taken steps to inoculate itself from legal action over situations like this.