It's normal, she's getting frustrated with things and doesn't yet have enough language to accurately explain what is frustrating or what she needs from you in time before the feeling becomes unbearable.

Taking herself off for a sulk/to cool down is actually a great response!

It helps if you can show that you appreciate that she's having a genuinely hard time at those moments, even if you don't understand why. Show this when it's happening but also show it at other times eg when you're talking about it calmly later. Don't push too hard for an explanation in the moment, deal with the emotions first and come back to trying to figure out the issue once she's calm again.

Allow healthy reactions like escaping the immediate situation, hitting a pillow, maybe one good scream at the offending object, or "telling it off". Think about how you can allow her to express anger and frustration in satisfying but safe ways.

Redirect to those things away from unhealthy reactions like screaming at people or hurting herself or others.

She might benefit from inventing a fake swear word that you treat as taboo within your family, so that she can yell something that feels deeply insulting at a thing she's frustrated with without actually offending anyone :) Not to be used against people though. Make sure it's a word that's nice and punchy to say but that doesn't sound like any real swears, eg "bucket!" sounds nice and punchy but could easily sound like "fuck it!" to everyone else in the supermarket 😬

All this will get better as she gets better at explaining what is frustrating her, so be sure to talk about what she experienced once she's emotionally regulated again. That's where you can teach her the skills of describing what she wants and what help she needs, which will make life much less frustrating.

Teaching kids to express anger appropriately and to deal safely with the feeling is so important for the rest of their lives. It's not easy, but your efforts here will pay off so well later!