Many prisoners sentenced in state courts serve time in federal prisons pursuant to agreements between that state and the Federal government. Laurel's "crime" violated Pennsylvania law, and she would have been sentenced (if at all) to state prison, but could have been transferred to federal custody for some or all of her time. States also sometimes have agreements with other states, and so Laurel could in theory have been serving her Pennsylvania time in a California state facility. But it's all highly unlikely if not ridiculous (the five years and not even looking for William, whom she could have found easily). Really terrible plotting.
