She should also check with her employer, some employers have deals with insurance companies, she may be able to get a group discount. She could also check online comparison sites to get an idea of average costs with other companies.
I don't know about the UK, but in Ireland, it is the law that if you are taking out a mortgage to buy your home, you have to take out life cover for the amount of the loan. This is then assigned to your lender, so if you die, the loan is repaid adirectly to the lender and they then don't have to chase your next of kin. It does mean that you can't just say you have the cover - you have to provide the policy schedule to the lender, and sign a deed of assignment saying that the payout from the policy has to go to the lender.
Lump sum critical illness cover isn't legally required for a mortgage - but is still really important. Particularly for a single person with only 1 income coming in - if she got really ill, at least her mortgage would be paid off. Her sick pay from work is good compared to the market, but what if she got a chronic condition and couldn't work at all for 3 years? I know at
Sometimes a lender, as a condition of a loan, will require that more cover is put in place than is required by law. Yes it makes it more expensive but if you ask anyone who has had to claim, they will all agree that it was worth it.
Oh, and if someone forgoes commission (i.e. as a favour to a friend/family) you are looking at a 5% to 15% reduction in premium usually.
In the interests of clarity I work in the insurance industry but not on the sales side.