I am thinking dont that you cannot feed her in any sense right now. Quite simply tell her that you are very sorry but you will be in touch when you are able or DH is able.
You absolutely must conserve your strength and energy for your immediate household and loved ones within it (I extend that to the hospital, not taking it too literally). Lots of precious energy is going on stress and upset with your mother and there is nothing you can do because you are not the problem.
The hospital team will have to tell her only to call at certain times and you can screen your calls. I may sound harsh but pray to God, she will really and truly cope herself if she needs to.
And I know it is hard when you are normally the organiser or cater, but please ask for help for yourself from those who give it freely. The shopping and meal issue is hopefully sorted with online deliveries, so the next question is what other practical help do you need? Is there any one at the hospital who will provide social support given you and your DH's difficult situation? Or a friend you can ask for lifts? I am always self-sufficient but sometimes you need help, and have to ask for it.
I am praying that you find some practical solutions, dont, and do not berate yourself for being annoyed with your mother. It is not unChristian to have some boundaries in place to protect yourself when you need it.
And feeling low is also fine. I remember crying once and DD asking what was wrong. I just said humans have weather systems too and mine was raining. Bless her, she then did something she knew would make me laugh. So we got my weather system to drizzle. Flowers and plants need rain to grow, so do we.