- If she sincerely repents of her fornication
- is reconciled to God and the Church in the Sacrament of Confession, and
- avoids situations where she might be tempted to resume the fornication:
Yes, she can receive Holy Communion.
If she is living with him in his house, that could be the sin of scandal but it is hard to say, with the information you have provided, whether that would preclude her from receiving Holy Communion.
We don't know the state of her soul or what counsel she received from a priest, so we can't really judge unless we have evidence from her own mouth that she is unrepentant of:
- what she knew was a grave sin
- that she fully consented to it, or
- that she did not confess this in the Sacrament of Confession.