I drive a 15yr old car, have been driving 40 odd yrs without incident (touch wood!) yet insurance companies now suddenly see me and my old car as a risk and quote exorbitant amounts, that's the ones that will even quote. It's the same with life insurance, they are very adverse to any perceived increased risk, it's a sort of blanket ban on certain things, the individual nuances of each case don't come into it. Don't get bogged down in the fact that she has been refused everywhere, I know it feels like a personal attack and somehow sinister but it isn't really, it's just the way insurance companies are.
Seriously, just ask your bank, this is very common. Your solicitor is going to tell you the same thing as they don't know where you are going either at the moment without knowing if the bank is ok with a waiver. It's a very straightforward issue for the bank, they have pre printed forms for it. The only risk is that your bank is one who has a stricter policy on waivers but even if they say no initially and I don't believe they will I would ask the person you are dealing with to appeal that decision based on the percentage of your wifes salary compared to yours in the calculations.
You need to do this first, once you have the banks ok for a waiver then you can shop around again for the cover but a waiver will leave you free from the banks requirements so that instead say of having to take out cover for the full mortgage over the full term which might be totally unaffordable even if you could get it, you could alternatively take cover of say 50k for 10 yrs or whatever was doable.
I want to see here tomorrow evening that you have asked your bank, pretty please