9 year old...puberty?

My daughter turned 9 years old in November. In the last week she's mentioned her breasts feel sore/tender. Her right worst than the left. Is this puberty already? I just did some reading online and it says at age 8-12 years of age her breast buds are developing. And about 2-3 from the breast buds developing, she may get her period. She seems so young still. 😭