Instead of ignoring it I would show compassion. With her behaviour she’s communicating something and clearly something is upsetting her. I would show understanding, have chats and spend time with her.

It could just be a phase. Perhaps something happened in her life at that point in time (another sibling???)

Slapitsole.

I’m praying it’s a fade because mine has been the same.

That sounds concerning for you.
Another idea – if you know why she is acting sooky (like wasn’t allowed something) maybe start by putting words on her feelings for her adn then giving her an alternate behaviour. Like ‘wow you seem upset I wouldn’t give you a lolly. When your’re ready you can have a banana or apple.’ Or ‘you seem upset, when you’re ready you can help me do some cooking’. And give her time to be sooky, then give her attention when she’s less sooky.
And if she uses a sooky voice to request thing try gently asking her to use a normal voice if she’s requesting something then give it to her once she does.

Wow.. that sounds difficult. I’d read and ask around for more advice but would personally tend to try and ignore it …. based on the idea that getting attention for something unwanted might only stimulate it to happen more because of the reaction it gets from you. ….I think it’s important to remember that children aren’t adults too … and not to expect every question to be answered (sometimes they really are processing something) and might not realize that you are speaking to them or that looking at you is the social norm (sometimes she might get it but not other times)…I wonder why she does it? (other than perhaps to get some attention).. and whether it happens to others/peers or just you? would certainly encourage her to use words to explain what is going on, perhaps when she is in a good mood so that the interaction doesn’t generate attention at the wrong time! And try and catch her in the good moods to reinforce the interactions that are more socially acceptable.