If you sense that she's actually losing language skills then I would take her post-haste to the pediatrician and get a speech assessment or an assessment for ASD.
Don't mean to diagnose - just when someone says their child's language skills changed in a regressive way when they were a toddler, my ASD antennae quiver.
Oddities of speech that seem "out of her control" should be taken seriously in my opinion. I think some of the suggestions offered have been really good ones and you should try them but if they don't work it may be time to consider alternative explanations.
rlsnights ... you are absolutely right about the regression in speech linked to ASD but I really think what is being described is more of a phase for attention then anything else. Now things to be on the look out for is words that she used in the past disappearing from her vocabulary and new words in the place of those... such as the nugget example... if she could always say nuggets and reverts to a baby word and only uses that or similar words to ask for the nuggets and has lost the word nugget altogether than yes it is a red flag for possible ASD. But as it has been described she seems to be play acting in a baby state and uses the baby talk during that time period and if that is how she is behaving it really is more about a phase. Has there been any thing big and new in her life? Might be a new school or a close friend to her has moved away and of course a new addition to the family and again it can just be as PTP and Neato described about the age and realizing they are becoming a 'big' girl/boy and exploring the 'little' girl/boy category.
