Why does my 9 month old act like a toddler?

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I’m really confused and really don’t know how to handle her atm She is 9 months old and she acts like a toddler! Screams when she doesn’t get her way! If you take something away from her she screams! If you want to eat something for herself she screams and unless you put food down for her. When runs out of her puffs she fusses. I have not done any discipline obviously cause she so young. I do the occasional stern “stop” or “no” and that’s it