Can you recommend some very basic books for a 69-year-old widow who is now having to manage her money?
Yes, there are some great options out there.
If you haven't taken your pension yet, the Money Advice service has some free downloadable retirement guides which are sent out by quite a few pension providers in their retirement packs. They cover pension options and things to consider in a clear language.
Which has a booked Called Money in Retirement. I always advocate the Which guides as they write in a clear language.
The Good Retirement Guide 2018 by Allan Esler Smith covers a wide range of topics that impacts on retirees and it useful suggestions for retirement that you can refer to.
Retire in Style is a magazine by Moneywise. It's very visual and offers good explanations of a wide range of topics relevant to retirees.
I hope this helps.