How do I know if my daughter is going through puberty?

Breast development. Breast budding constitute the very first signs of true puberty in girls. Pubic or axillary hair can develop soon after or sometimes earlier depending on genetic background (extra weight can also be influential).
Breast budding. That is the earliest sign of puberty in girls. Normally this shouldn't start before age 8 years old. Pubic hair is a separate process which coincides with puberty but comes from different hormones. Earliest age should also not be before 8. If you notice any signs of secondary sexual characteristics before she is 8, please take her to her pediatrician.