Why is this religious sentiment socially acceptable?

Yesterday my grandpa (who helped raise me) was diagnosed with inoperable cancer. When my mother-in-law (an evangelical Christian) found out about this, she said that she hoped that my I would “come to know Jesus” through my grandpa’s illness. From what I can see, this sentiment is quite polite and socially acceptable.

I’m an atheist. Imagine if the situation were reversed and I told my MIL that I hoped she would lose her faith in God through having one of her dear relatives die of cancer. I can only expect that this would be seen as an insult of the highest degree.

Why is it perfectly OK for her to evangelize me through this tragedy, and I am expected to thank her for her concern, yet the reverse would be a slap in the face that would make even my atheist friends wince?

Please note that this is not a debate about God’s existence. I’m sure there are plenty of those in the archives that we can reanimate if need be. This is more of a question about social and religious etiquette.