Using your child's disease to preach/shame people?

Recently a teenage girl I know was diagnosed with a rare disease. I'm not going to say what it is for privacy reasons, just that she's currently in the hospital getting treatment, it's not cancer, and from the research I've done there's like a 80ish% 5 year survival rate.
There's a post on Facebook from a few days ago made by a family member, they basically said that people who weren't the same religion as them were praying "wrong", and that they need to "repent" and convert to their religion, so that their praying would "work". This was mostly targeted at people of different religions who were already praying for her. I thought about posting a screenshot of the post, but for her privacy I won't be posting it.
What are your thoughts on this?
My two cents:
I think it's extremely rude to use your kid's disease to tell people that they are "sinning" and "going to hell", and it's just gross. Not to mention extremely illogical. People aren't going to convert to your religion when you're rude to them. 
I'm an atheist, so I'm not the best person to know this, but since when does the amount of people praying for your child they "right way" have an impact on whether it works or not?? If I was a theistic person I'd want people of all religions to pray. Like, in the event that I was wrong and my hypothetical religion isn't the "right" one, then there'd at least be someone who was doing it the "right way".

Vote below to see results!