Have you thought to just ignore it, maybe it is getting a reaction from you, the more you make of it the more it becomes.
Actually she is the one always asking to do homework and yes, she's quite a competitive little girl. She uses gibberish when I ask her difficult questions like, "Did you hit your sister?" or "Did you or did she have the toy first?", so they're not difficult academic questions but difficult situation questions where she knows she has done something wrong, but instead of saying, "Yes, I took the toy away from her", she says gibberish. Basically, I think she has a very healthy ego and does not like to be wrong, so this is her way of coping. Instead of admitting she was wrong, she says, "This is MY language for saying yes, or no, or whatever the case may be that requires me to say something embarrassing". She's even admitted that "I'm answering you in (her name) language!"
Margypos, my 3.5 yr old is already past the gibberish babytalk stage, so I don't think my older girl is trying to get more attn. In fact, I think she's trying to shift attn from herself when she does that, as though she wants me to give up trying to make sense of it. I dunno...I've asked her to only use gibberish in her makeup music (she likes singing nonsensical songs) but not when I'm trying to talk to her about something serious because I tell her firstly, it's not funny and secondly, I don't understand the language. So far, she has complied quite willingly.
I just want to be sure I'm not making it worse!
Is she being called to task for things she really doesn't know the answer to? I've seen kids do this when they're kind of overwhelmed by discipline, or if they're overwhelmed in the classroom and they really can't understand the subject but keep being forced to answer "do you understand". It doesn't sound like academic difficulty is the case with your daughter because you describe her as very bright, but could she feel under the gun all the time?
Imagine watching a video of what goes on in your home - would it look like you're on her all the time?
She sees the 3year old getting attention and she is acting younger to get the same quality of attention,its baby talk nothing wrong with your daughter she just wants more of your time, how about some one to one time for her whilst Dad has the younger child tehn switch so Dad is giving her some fun and Games,Dont correct her when she talks Baby talk just ignore it no issues over it.when she does it dont respond , and if she is having fun well we all need a dose of that sometimes.
Just to add, her little sister is now picking it up. I don't want to curb it if it's harmless but if it's an indication of something I need to pay attn to, I want to know why and how.