Daughter refusing to speak normally

YABVVVVU to use the expression 'broken home' in 2024 for a start!
Also, as a parent to a 9yr old autistic DD who does exactly the behaviour you describe, I'm saying that your DD very much is neurodivergent and that it's nothing to be ashamed of! Unless she's been assessed by the NHS and you have it in writing from them that they've found her not to be neurodiverse, then you cannot simply declare her as "not neurodivergent" as you don't have the power to say that. Even child psychologists need a panel of fellow child psychologists and autism specialists to declare a child to be one way or the other.

Have you actually sat her down and asked her if she could explain why she’s doing this? And what did she say?

I’m also interested in how you know the baby talk is the reason her friends seem to be dropping her. Have they told her that? Have their parents told you? Or is it a guess?

I think it is relatively common for kids to go through a phase like this, but maybe not as extreme as it seems to be with your daughter. I do think ignoring her unless she speaks normally is probably a good idea.

Oh god-one of mine did this! Drove me mad. My mother advised me to just ignore it-and I did. And she stopped.

No possibility anything unpleasant has happened to her that you're not aware of? If you were there during child psych assessment she might not have wanted to talk about it. Assuming this, and that you're confident she's not ND, sounds like one to just ignore. Bit odd that she's driven her friends away by doing it is the only reason I ask about other things. Has she discovered that doing this gives her some power over other people's behaviour, even if negatively, so she's testing that out?

Sorry, just saw you've already attended a child psychologist. What did s/he advise?

I think this is a recognised phase that some children go through, sometimes because they are anxious about something in their life. I once taught a 10yo girl who did it. It's very annoying, but they do grow out of it! It might be better to ignore it.

I feel sorry for your child.

Agree with this.
Behaviour has a reason behind it. You need to identify the reason. Are you sure she's not ND? (How can you tell? Girls are often late to be diagnosed.) Are there any other behavioural issues?

I'm sure I read before when children do this it is because they are realising they are letting babyhood go and aren't ready to not be a baby/toddler anymore or I suppose a little child and they are coming to terms with it. Apparently it's also linked to needing more attention.

Did she discuss the baby voice?

By any chance is she looking for kindness and understanding from you ? You seem to talk about her quite harshly ?

Ignore it, not in a dramatic way - just ‘darling I don’t understand you, speak normally’ and then carry on till she does.

She won’t do it to her teacher

They go through weird patches and she’ll probably knock it on the head when she’s back at school. If she doesn’t then seek some advice from the school counselling service on how to manage it while it lasts. It’s not easy.

I think you need to seek professional advice. To me it seems like there might be a bigger issue and your daughter is a very unhappy person for some reason.

Mines been barking for two weeks, i almost snapped yesterday. It sounds really really annoying. Perhaps a serious sit down chat would help. Be clear that it’s not cute and not endearing and is actually quite annoying, does she understand this and if so why does she continue to do it. I know that sounds a bit brutal but maybe she needs to be told outright before she goes back to school and really starts annoying her friends.

Other option is just ignore anything said to you in a baby voice.

She's deep into role play. I used to work at a girls' group and one of the girls spoke like that almost 90% of the time. She too was NT as far as I could tell. I think it's just a phase and you have keep reminding her to speak in her big girl voice.

I understand your frustration. It used to annoy the fuck out of me.

don't be daft - plenty of people speak another language. It's what i did when my DCs tried talking strangely to me (sort of nearly but not quite gangsta)

I spoke a language they don't understand and they soon stopped.

I would actually take the kid to child psychologist. It is possible that there may be an underlying issue you are not aware of.

Oh, I forgot under the trauma of remembering the Mancunian Phase.

The other one decided to speak Cat for a week. I already had three of the buggers yelling at me throughout the day, so one more without fur didn't really make that much of a difference. She changed her mind pretty sharpish when I carefully flea combed the real cats and then went to use the same comb on her.

if you speak another language, only speak to her in that one. Tell her, once, in English that as long as she is talking in a language you don't speak, you will do the same to her.

This made me laugh - nothing the OP has said suggests she speaks another language.

Baby TV only. Baby food. Early nights. Def no WiFi..

Well, bedtime is 6pm for icky wicky babies, isn't it?

I'd tell her sharply that she either stopped with the baby language or I'd treat her like a baby. None of the privileges that 8 year olds get.

Don't engage. My 9 year old went through a period of this "me can't do it" and stuff like that. I just told her I didn't understand her when she spoke like that and wouldn't do what she asked until she spoke properly.
She snapped out of it sharpish.