The 65-year-old actress, who played Pauline Fowler on the BBC One soap, was diagnosed with an aggressive form of the disease in January this year. She has previously fought breast cancer twice.
"I went for my usual annual check-up and they found that some cancer cells had returned in my left armpit," Wendy explained.
Richard told the Sunday Express newspaper that she has already made out her will and discussed plans for her funeral.
"The drugs I was given to help had an adverse effect. If anything, they did more damage than good so my health has really deteriorated," she continued. "Now I have a cancerous growth on my right kidney and the cancer has spread to my bones.
"Twice I've had breast cancer but this is different. It's more aggressive this time, unfortunately, and has spread to the top of my spine and left ribs."
Richard plans to marry her partner John Burns before starting a course of chemotherapy later this month.
"My oncologist said I've got several useful years ahead of me but since then it's got worse," she said. "Part of me is dreading the chemo but I've got my wig all ready and prepared, because obviously I will lose my hair. Because I've never had chemo before they can give me a big dose so I'm hoping that will zap it."
The actress starred on EastEnders from 1985 to 2006. She had previously played Miss Brahms in Are You Being Served? for thirteen years.