If DB is not talking, and since your DF died, you need help. You don't say whether your mother is able to cope alone. You do her shopping but do you have to? Online supermarket delivery is great if she is able to put it all away herself. If she is dependent on some help then try to get that in place first before you act, eg carers, shopper, cleaner, weekly lunch club, and that will take some of the burden off your shoulders. Local authorities often have an alarm service. Find out if DB is willing to help sort things out. Maybe have a quiet word with the neighbours and get their opinion. Social services is a battle but, if she is entitled to help, be persistent. Otherwise, she may be able to afford it herself. If all else fails, would you pay for help for her for your own mental health?
You say her personality has always been like this. If she is also now worried about being frail and alone she will still use bullying and guilt to keep you running after her. Don't give her the satisfaction of arguing or reasoning with her. Maybe occasionally surprise her if you could detach yourself, pretend she's not your controlling DM, and say tell me about it, what are you worried about? Not that she deserves that from you but she might need to unload too and it gives you back some control. For this reason, I don't agree about not giving her a time when you will phone, for a person living alone it gives some consistency, for example, 'Gampsy phones me every Tuesday evening and visits every other Saturday for an hour' and that is a constant for her.
Try to take the burden off your shoulders now as much as possible- unfortunately, given her age, things will only get worse. I love the grey rock advice - I found this was one thing that worked with DM. If she said something inappropriate I changed the subject none too subtly sometimes! DM had a very hard life but I never really wondered about how the war affected her, as someone else said. I'm sure we have lots of imperfect mothers amongst our numbers too but that generation lived with the horror of war and fear so I guess being aggressive or unable to be loving and warm might have been a consequence of that. Not that that makes a difference to how you choose to deal with it. You sound a kind person but don't just put up with this situation, take your thinking time during your holiday and work out a solution for both of you that will free her hold on you and prevent you feeling guilty. If you decide to cut contact with her, remember it was imposed on so many elderly people in lockdown and she will manage.