This OP. It’s a big red flag.
if she’s otherwise competent, helpful and independent then there’s something around food going on.
Does she not like touching it.
Im suspecting some form of AFRID.
What are her eating habits like. Is she picky.
Pizza is a classic beige food which a lot of ASD people are happy eating but there can be a lot of internal rules in her head about how food is presented and how she must consume it.
The fact she’s rather go hungry suggests there’s some sort of rule in her head about how food must be presented before she’ll eat.
You don’t know what those rules are, even she may be unaware of them.
The sensitive scalp is another giveaway about sensory issues.
Im not sure how you probe into this carefully.
Maybe you could just ask her if the plate is very important to her.
Asking her why won’t do much good but ask her about the place and see what importance it holds.
It may be very very important. In a sequence of steps. So it may be early sign of OCD.
Your DH is right that you should get a plate.
But you need help externally as this may grow.