Worried about child not eating

[SkinnyMaLynx]

I can't get the foods my DD will usually eat and usually (because of the peer aspect I think) she at least eats most of her school dinner. The last couple of days she has eaten almost nothing. We are self isolating so can't go out and the people who've been helping us get groceries cannot find any of DDs safe foods either. My last shopping delivery came with most of it missing and all of her items. She was eating something from all the food groups before (just about) but now is basically just eating plain carbs. Plain pasta, bread (no butter), cereal (without milk), supernoodles (without the flavour packet), etc. How long can she eat like this without getting unwell? It's not a medical issue exactly, not even sure it's mental health but couldn't think what else it is? We've been waiting a long time to get some help with this and now it's escalated at the worst possible time