Is a deceased sister who delayed prayers due to an illness that prevented her from performing ablution, and then died before recovering, considered an infidel, despite her having given charity and paid zakat? And is it permissible to make up the prayers on her behalf, and how?

It appears that the sister stopped praying due to her illness, unaware that prayer is not waived for a sick, adult, sane person. We hope she is excused by Allah. However, if she abandoned it intentionally, knowing its obligation, out of laziness, then scholars have differed on whether the one who abandons prayer commits major disbelief or minor disbelief. It is not permissible to make up the prayers on her behalf, for prayer is a purely physical act of worship that does not admit proxy, except for what has been explicitly stated in religious texts, such as Hajj.