HI,
If she has been absolved of that sin, of course she may receive Holy Communion. If she was baptized after committing the sin, that sin would have been forgiven. If she were already baptized, then she would have been expected to mention it at her first Confession. If not
she forgot to, then it was forgiven, but she needs to confess itas an expression of her repentance.
Fr. Vincent Serpa, O.P.