One thing I would not do, is to keep harping on the fact that "you are a big girl....", because, that to me, just exacerbates the 'stress' of it all.
And makes it worse.
The more you push the idea, the more the child will regress. It is too overwhelming... per emotional maturity of a mere 2 year old.
They have NO coping-skills at this age nor any fully developed emotions, yet, at this age.
Constantly being told "you are a big girl...." just makes it more overwhelming. Especially if she is not ready for all of those 'expectations.' And per developmental timelines.
Keep things simple.
Let her express herself.
But don't bring too much attention to it.
Distract her.
Just give her other things to do.
Give her a Dolly to 'care' for.
Show her you identify with her... that you are getting used to baby too. So you 'understand.'
She needs validation.
She needs, feedback... that makes her feel good, not inadequate or immature. Which always being told "you are a big girl..." can make a child feel 'inadequate' especially if again, they are not ready for that.
Kids this age, will not necessarily KNOW what being a "big girl" is. All they know is what they feel are think. She is, only 2 years old. She is not yet, an older child.
Keep expectations, age-appropriate.
This phase, will pass.
It is not just about doing activities with her... but talk 'with' her.... about stuff. Anything. Her feelings and validate her. Their ideas/fears/stresses/worries, are that of a child. Not an adult.
Help her feel, she is "okay."
My daughter needs chats... to feel 'bonded' with me. So I do that with her. It helps.
all the best,
Susan