YOU SAID:

Assuming that she is innocent, (a fact I sincerely doubt), she would need to pay her debt to society for many years.

INTO JAPANESE

彼女が無実であると仮定すると（私が真剣に疑う事実）、彼女は長年にわたり社会に借金を支払う必要があります。

BACK INTO ENGLISH

Assuming she is innocent (the fact I doubt seriously), she has to pay debts to society for many years.

INTO JAPANESE

彼女が無実であると仮定すると（真剣に疑う事実）、彼女は長年にわたり社会に負債を支払わなければならない。