Two non-Catholics marrying in Vegas is a valid marriage. The Church views this as a valid marriage unless and until it is proved otherwise. The couple obtained a civil divorce but that doesn’t end the marriage.
This all should have been addressed before she came into the Church. Usually, in such cases, the first marriage is looked at to see if it was valid and an annulment can be sought before the person is welcomed into the Church.
It sounds like someone dropped the ball with this woman’s preparation. Perhaps she is just finding this out now.
The Church isn’t telling her not to have sex with her husband. But the deacon likely affirmed that her current marriage is invalid and that she is considered still married to her first husband. Now that she knows, assuming that this wasn’t brought up in RCIA, one way to keep receiving the Sacraments is to live with her second husband as “brother and sister” at least until the first marriage is investigated in an annulment process.
While I am sure there is a lot more information than is posted here and more even than the husband may have shared with you, it isn’t “baloney”. It’s a sad situation that many people who are divorced and remarried find themselves in. There are no easy answers but resolution is not hopeless.