Is it permissible for the wife of a man afflicted with dementia to give a portion of her lawful money in charity with the intention of replacing part of her husband's charitable donation to the mosque, which originated from bank interest, while also spending a portion of the bank interest on public projects?

A wife is not permitted to dispose of her senile husband's money. What the man did by donating his money for the expansion of the mosque before his senility is a valid and enforceable act, even if some of the money came from usurious gains, because it serves the interests of the Muslims. Neither his wife nor his guardian has the right to take any of his money to give it as charity on his behalf.