Trying to find travel insurance for my mum so she can go on holiday. She recently started chemo for endometrial cancer

Mum has recently started her chemo for endometrial cancer. She is hoping to get away for the first 2 weeks in November before she starts her radiotherapy. Her Dr is totally onboard with it. I have been trying to source travel insurance for her but I have nothing coming in under £1000. Does anyone have any suggestions?? I have tried Medical Travel Compared, Staysure and Avanti.