The tumour had broken through the lining of her bowel but there was no evidence of it spreading further, she said.
On Monday she would start six weeks' treatment of both radiotherapy and chemotherapy, followed by surgery and a second round of chemotherapy.
It was a daunting few months ahead but she said it was the biggest comfort to know she would not be going through it alone, as she had to do with a lot of things as a single mother.
Her childhood friend Melissa would shave her head in solidarity.
Ms Clare said she was overwhelmed when Mrs Howell told her she wanted to shave her head for her.
"It's a huge relief to not have to go through it by myself ... I think I've been really lucky because I haven't felt that panic or isolation people feel when they're going to lose their hair because I know she'll be going through it with me."
Mrs Howell had organised for her hair to be shaved by another friend at Shine Hair Salon in May, and all funds raised would go straight to Ms Clare.
Ms Clare said it was hard to accept money from people but was grateful to have support with the "huge financial burden" that came with cancer, that people often did not think of.
Mrs Howell said as soon as she heard of her friend's diagnosis, she wanted to help.
"She thought I was crazy ... I said 'it's just hair, it'll grow back'. We'll be the sexy bald girls together."