Perhaps you and your MIL are victims of simple miscommunication.
Some people have devotions to particular saints, or to the Blessed Mother.
Naturally, they pray to God daily, and at church–as has been pointed out, the entire Mass is a prayer to GOD.
And, in ADDITION, they pray to their favorite saint, and through that saint, to God.
Perhaps your MIL was trying to tell you, if you objected to her praying, say, to St. Joseph, that she prays to St. Joseph ONLY in order for him to then intercede (which means something a little different to a Catholic than a Protestant) with God. With a Catholic, we know that Christ is the ONLY mediator between us and God. . .but that doesn’t mean that we–living and dead alike (for the dead are with Christ and live with Him eternally)–can’t intercede for each other, just as you might ask your fellow Mormons and your pastor to all pray together for some fellow Mormon who was ill, or in trouble.
Could this be a possible explanation?
That your MIL has a devotion to a favorite saint, and that through his or her good example and prayers, she is drawn closer to God?