The Book of Being — Ian Watson

The megalomaniac Godmind is still planning to use all the minds in creation to make a vast 'lens', and if necessary it will burn out all life in the process.

Back beside the river and literally born again, Yaleen represents to the guild of riverwomen the perfect proof of salvation, of life after death. In fact, she is desperately searching for a way to save the whole universe from imminent destruction.