You can send her a voucher for Cook. They do very good quality frozen meals and deliver to most of the UK so she can order what she fancies.
Keep sending messages, and tell her there is no need to reply.
When you go to visit, take easy to eat food with you, something like a cooked chicken, a quiche or soup. You have no appetite, but if something can be picked at from the fridge at least it's fuel.
Keep in mind that it's virtually impossible to make decisions in the immediate aftermath and shock, so don't expect her to tell you what she needs you to do, instead offer. e.g I'm going the supermarket on the way over, what can I get you? Let me put the hoover over when I come round etc, that sort of thing.
Expect her to be exhausted, I had no idea bereavement was so tiring, and sleep didn't often find me.
Keep any platitudes to yourself. So no 'at least he didn't ( fill in the blanks) ' or 'he's your gaurdian angel now' unless you know for sure she has a strong faith.
And above all, keep on keeping in touch.