It's horrible. Especially around new baby sister. He ends up waking her up and I'm losing my mind
I agree with having a snack or starting with breakfast, my son is a monster until he actually eats something
Taking time to fill up her cup first thing in the morning. Just a couple minutes. Connect. Something like cuddle, read a book, talk about what she dreamt about, etc. then move on with the day. Get her involved if you can, get her help making breakfast or unloading the dishwasher, etc. give her a job or an activity to do. Reward good behavior and quickly correct bad behavior. I have my son take responsibility for whatever his bad behavior was, that might just look like telling me sorry, wiping up his spill, having him say what he wants the right way instead of whining, etc.
I started having a morning snack available! Mini muffins or meat sticks in the room, first thing! My kid was hungry. And I tried to make sure there were as little power struggles as possible. Even if that meant slowing down, not getting dressed till after eating, etc. etc. Sometimes the tantrums are unavoidable, you're doing great!!!