Hi,
A couple of ideas...
She may be so hungry she gets herself worked up, Perhaps try feeding her more late in the day so she might not get so hungry in the morning. maybe add more protein and fat to fill her tummy.
She may be becoming unwell, sore throat, or sore tummy before bowel movements. Eating tends to encourage bowel movements.
She may be pushing her boundaries. Every kid will throw stuff off their table, the more attention given the longer it can last.
She may dislike her high chair, and want the independence to eat at her own table. If that's the case, just go with it, and encourage to sit at the table to eat rather than walk around. She might be frustrated that she can't play and eat??
She might like a new type of breakfast.
You can't really discipline to stop tantrums at this age, just do anything to avoid when you can, re-divert. Perhaps try distracting her out of a potential melt-down. TV on, or a toy, or chatting about something you saw outside.
The tough bit here is that she is really hungry, and an upset hungry child is tough!!!
