What does it feel like to not be able to act on the impulse?

I apologize if I'm in the wrong sub, and please kindly direct me where I need to go. I don't want to intrude.

I do not have ADHD, but I highly suspect my 7 year old daughter has it, specifically the hyperactive-impulsive type. We're starting the process of getting her diagnosed. It might take a while before we can look at medication. In the meantime, I thought it would be good to post here so I can hear from women that can articulate the thoughts and feelings my daughter is having.

The biggest thing she struggles with is impulse control and emotional dysregulation around that. Like she'll get an idea in her head that she wants to do something or wants something in a certain way, and she doubles down. It's like she has a compulsion to do the thing and if she is blocked from it, it's a meltdown.

A couple of examples:

1. My husband dropped us off at the pool for my 4 year old son's swimming lesson. My daughter wanted to come along to watch. It was quick getting out of the car and at the last second she decides she wants her backpack (that has nothing in it, she just wants it). My husband's tosses out what he thinks is the backpack and drives away. We realize it's a different bag, and she melts down screaming, trying to run away, etc. for the next 1/2 hour until he picks us up again.

2. It's dinner time and as we're walking to the dinner table my daughter is talking about a chore chart she wants to implement. I say that's a great idea. She then wants to start working on it right away. I say why don't we work on it after dinner, we can write the idea down and talk about how we'll do it during dinner. I keep her from accessing the art supplies and it turns into a tantrum. I have to bring her to her room (calm down space), and she goes through the tantrum wave. Finally after calming down, she comes down for dinner and the chore chart never gets mentioned again.

I want to know how to better help her regulate in these moments when things aren't going her way. For those of you who struggle with this, or have in the past, what do you think is going through her head? What is she feeling inside? Anxiety that things aren't perfect? Need for control because she wants autonomy? Or is it like an itch that needs to be scratched? I guess I just want to to know what is driving that impulse and why it might feel catastrophic when she isn't able to have it her way.

Any insights you can provide are welcomed. Thank you so much.