I'm not an expert at this, but the only reasonable way to get to the Canaries is by flying, and that might not be wise, due to the reduced air pressure in the aircraft, and the possibiity of cross infection from other travellers in the crowded conditions of a typical charter flight.  

So I wouldn't travel unless advised by a competent doctor that it's safe to do so. 

If it's not safe to travel, then if you have already got travel insurance you should be able to claim the money back for all parties, and find a suitable spot in the UK for a holiday. 

Hi, I'm so sorry about your mums health problem. I know exactly how you feel. I had to cancel my holiday the day before I was due to fly, it's so disappointing, my case was packed. To be honest I would not have enjoyed it as I would have been worried sick the whole time I was away. I had to go for lots of tests before any treatment took place and all this would have been delayed. Also a lot of firms won't insure you at that stage of diagnosis, they want to know loads of information which I couldn't give them at that time. Two years previously, I had a lung problem and again had to cancel a holiday (I seem to be allergic to holidays) lol. My consultant said I couldn't fly as the pressure in the cabin would not be good for me. I did get part of my holiday  refunded this time as I had insurance, but didn't with the holiday this year as I was still under investigation and didn't know what was wrong with me and really had to wait to let insurance companies know. I believe from what I've read it is very expensive to get holiday insurance now that you have a diagnosis of cancer.. I hope your mum can cope with this, it's not a nice situation to be in. I'm just looking forward to next year now and hopefully will get a wee holiday then.

Thanks for your reply’s everyone.

its all very raw and unreal and especially that mum has no symptons that she can feel, see etc...

its a totall bolt out of the blue?!

we will see what the professionals say after their meeting on Monday and then see what the insurance say..

i will come back to the forum with any updates x

Be wary that they don't excude her cancer from any cover they quote you for. 
Get two or three quotes insurancewith.com and essentialtravel.com are usually competitive. 
All travel insurance companies will ask whether your doctor has approved of the trip - so it is worth getting that in writing before you go.

Good luck
Dave

Thank you Dave

im going to try my very hardest to get my mum on this family holiday so all tips are greatly appreciated 

xx