The FBI detained her because she and her husband Harvey had one-way tickets to Vietnam (a country that has no extradition treaty with the US). State prosecutors have now announced they are going to charge her with murder, solicitation of murder, and conspiracy to commit murder - the same charges as her son Charlie was convicted on last week.
If she gets convicted too (as is highly likely), she will get life imprisonment. Prosecutors could seek the death penalty, but probably won’t (they didn’t with Charlie).