Who was Gurumayi Chidvilasananda?
A better question would be "Who IS Gurumayi Chidvilasananda?",
because as far as I know, she is still alive and well.
The following text is taken from www.siddhayoga.org
"Gurumayi Chidvilasananda is a Siddha Guru who walked the path
of yoga under the guidance of her Guru, Swami Muktananda. Gurumayi
received the power and authority of the Siddha Yoga lineage from
Swami Muktananda before he passed away in 1982. She teaches the
Siddhas' message that the experience of divine consciousness is
attainable in this human body."