Oh, OP, I remember those days when mine were little, unsettled and demanding, and my brain had just had it. It is OK to feel overwhelmed, and it is great your DH had them while you went away for a bit.
There are lots of things you can give/do with an active, inquisitive 4 year-old. When you have a little break, and some time to yourself, it would be worth writing a little short-list (5 things) for the next time you have one of those days. You can whip it out and give your head a little rest (rotating toy boxes worked well for us at that age).
For you little one, I think it is great you are still breast-feeding. Welcome to the extended BF club! On a day like this, it is probably exactly what she needs, as well as some alone-time with you. She calmed well afterwards, didn't she? And then had a whole banana! Good on her!
If you are concerned about her food intake, it helps to make a list of what she eats daily, and how much BF she gets. You probably already know that food comes first, and milk after.
If you find meal-times getting stressful, you could try some baby-led weaning. Put her in her high-chair with a sheet of plastic around it, and allow her to go for it. This will give her a little more control over how much and what she wants to eat, and if you can ignore the mess, it will ease your stress, too. In summer, we would put our DCs on the grass.
I think you are doing a good job, OP. Don't forget to look after yourself, too, especially after a wearing day. All the best!