First of all, conversion is the work of the Holy Spirit. It doesn’t have to be a slow, subtle process on your part, as you certainly don’t want your wife making a decision to become Catholic JUST because you urged her to do so. My RCIA director is emphatic that they DO NOT want people joining the Church just because their spouse/significant other is Catholic.
Not sure how old your daughters are, but something along the lines of, “I know Mom(my) was receiving Communion before, but the truth is, she really shouldn’t have done so because she isn’t (yet) Catholic.”
I would even ask her to think about going through RCIA to learn more about our Most Holy Faith. I know of someone who went through the RCIA program twice before deciding to convert, and they shouldn’t exert any pressure on her to convert before she’s led to do so. It’s a good place to learn about the faith, and I recommend that you attend the sessions with her if possible.
I also recommend the CDs from the
Bible Christian Society, if you think she’d give them a listen. (You can also download each one for free, if you get the CDs it’s just a dollar each for shipping costs.)
Recommended listening order:
One Church
Apostolic Authority and the Pope
The Bible and the Sacraments
and (to get this post somewhat back on topic) Marriage and the Eucharist - this will explain exactly why she as a non-Catholic should not be receiving Holy Communion in a Catholic Church.
HTH! I’ll be praying. My husband is in RCIA right now, and it’s totally a work of the Spirit!