"Joe and Jake are my stepsons. Niki is my husband's ex-wife and amazing Mum to Joe and Jake," she said.
"Niki continues to put them first throughout all of her treatment. Joe and Jake are also amazing big brothers to our 3-year-old daughter and she adores them as they do her.
"Money is running out and Niki may not be able to continue with her life-saving treatment.
"This is not an option - the boys need their mum and she deserves the chance to watch them grow into men and have their own families."
Hitchen was "completely overwhelmed" by Clare's generosity.
"Everyone especially [Clare] has been amazing. I didn't think people liked me that much!
"The support I've been given is phenomenal, not just from my family but from complete strangers too."
Hitchen was admitted to hospital with pain in her abdomen and was told she had a tumour in her cervix.
Seven weeks later the cancer worsened from stage two to stage four.
But Hitchen said she decided not to lie down and let her diagnosis ruin her life.