Based on what I have researched, Iglesia de Cristo is a Protestant Christian congregation.
While your wife is a baptized Catholic, she shouldn't be attending any of the sacraments unless she truly believes in our faith and what the Church believes about the sacraments. In addition, attending a Protestant faith won't help her faith in the Church seeing most, if not all, Protestant denominations have misperceptions about what we believe as Catholics, if not a downright hostility toward our faith.
If she did believe in our faith, after the proper instruction from her parish pastor, yes, she could receive the sacrament of Confession followed by, after the appropriate instruction, her First Holy Communion.
That said, when Catholic's receive Communion we are making a public statement that we are in a Common Union which the teachings and faith of the Catholic faith.
If your wife is mainly attending a Protestant Christian congregation, she can't say that she is in a Common Union with Catholic teachings and therefore she should not receive the sacraments until or unless she wants to believe what Catholics believe about our faith while rejecting various Protestant teachings from the various Protestant congregations she has attended.
You can't believe in both a Protestant denomination faith and the Catholic faith at the same time.
For Catholics, generally, the proper order that one receives the sacraments is:
- First Holy Communion
- Confirmation, and optionally, based on one's calling or vocation:
- Marriage or Holy Orders, also known as the Priesthood, and at the end of one's Earthly pilgrimage:
- The Anointing of the Sick
I hope this helps,