B.C.
It's not a change in personality so much as it is a cognitive development.
She's at the age where she's noticing that there's a bigger world out there than she's previously thought about - and it can be overwhelming and scary sometimes.
I saw a toddler at the beach this year who simply lost it - she shrieked and cried about the sand (it wasn't hot) and water and insisted Mom carry her and not put her down.
And the Mom was like "She just loved the beach last year and had a great time. This year it's not her thing at all.".
Our son was about 4 when we had him in Little Gym.
He had lots of fun.
And then for the last class all the parents were there with all kinds of cameras - and suddenly he had stage fright and would NOT leave my lap for the whole class.
They do figure it out eventually and their confidence returns - but the phase can last a long time.
As for the whining and complaining - how much does she hear from others?
Do they get attention for doing it?
Well - she wants in on that action - so she's coming up with complaints of her own.
Try to ignore complaints/whining (from her and everyone else) and when she's not doing it THEN lavish her with attention and praise.
"You put your bowl on the counter for me - what a wonderful helper you are!" etc and so forth.
Positive reinforcement should help her lose the whining habit.