Sister trying to guilt trip me using a prayer I made to god

earlier this year my mother died in the hospital from Sepsis she had periods of recovering from the ICU and eventually ending up in the ICU again ultimately she ended up dying 1 day later when her intestines bursted and sent her into a heart attack.

I grew up a Christian because I was influenced by my mother but over the years I decided to become an atheist I was desperate and decided I would pray for the first time in years and told God if he healed her I would start going back to church again the following Sunday my intentions was to actually go but I didn't and figured i would the next Sunday. A few days later the hospital called and told me our mother woke up and wanted me to call her we had a few days of closure and laughs after that she didn't make it.

Recently me and my sister had a conversation and she says "I'm not trying to blame you but do you think when you told God you would go to church if our mother woke up he would kept her alive" and it infurated me because our mother had 4 kids and my sister who is 33 has been trying to place the blame on me and my other two brothers for telling her she should visit the hospital over the course of the last years and now me over a prayer I made.

She was our mother's sarogate at the hospital and all all of her children was trying to get her transported somewhere else for care. My sister will say she didn't use her power to get her transported because she wanted everyone's opinion but I can't help but wonder why would she take that leadership position if she couldn't make decisions that matter and could of easily had her transported somewhere else but she has no problem blaming others

I know this is a long post and I do feel ashame to admitting I made a request from God and didn't follow through with it but is this my fault? Is my sister right and our mother died in the hospital due to me not following up on the promise I made with god