I am so sorry for the tragic losses in your family. My understanding is that salvation is a work done wholly by God through His Son Jesus Christ.
The scripture says in Romans 8 paraphrased: nothing can separate us from the love of God in Christ Jesus. Therefore mental illness and suicide cannot separate a true child of God from His love.
Whatever the Church’s decisions about where our mortal remains may be buried, we can take comfort that the destination of our eternal souls rest at the sole discretion of a holy, gracious and loving God who knows us and accepts us in His Son Jesus Christ.
I’m surprised they didn’t bury her. The contemporary thinking is that we really don’t know what that person was doing - did they repent at the last moment? Was it too late to go back but they wanted to live? Did they have a mental illness?
The better answer, fortunately, is charity. “Betwixt the stirrup and the ground, I mercy asked, I mercy found.” We don’t know what happened.