Kommentar zu Niddah 5:8

איזו הוא סימניה (what are her signs of puberty) – it is referring to צמל/the stage of complete puberty in a woman.

What are the signs [of a bogeret]?
Rabbi Yose the Galilean says: the appearance of the wrinkle beneath the breast.
Rabbi Akiva says: from when the breasts hang down.
Ben Azzai says: the darkening of the ring around the nipple.
Rabbi Yose says: [the development of the breast to a stage] when one's hand is put on the nipple it sinks and only slowly rises again.
Today's mishnah contains several opinions as to what constitutes the physical development of a girl such that she is considered a bogeret. All four of these opinions relate to the development of the girl's breasts.
I think that the translation of these four opinions is sufficient to understand them, therefore there is no commentary below.

קמט – her breasts grew until they are folded a bit upon the chest and they appear as a fold.

משיטו דדיה (that her breasts hang down) – they are larger than a fold.

הפיטומת (when the surroundings of the nipple begin to grow dark) – the top of the breast, like (Tractate Sukkah, Chapter 3, Mishnah 6): ניטלה פטמתו/if the pestle-lie protuberance of an Etrog is taken out.

על העוקץ -point of the nipple that the baby sucks on. And the surroundings of the nipple which is around the point, and all of these signs of puberty when they are appear in a woman, she is an adult. The one in accordance in with the opinion he holds (i.e., for example, Rabbi Akiva) and the other in accordance with the opinion he holds (i.e., for example, Rabbi Yossi), but furthermore, the father has no authority/control over her. But the Halakha is according to the words of all of them in the strictest opinions. Therefore, it one of these signs of puberty appear on her, we judge concerning her the law of an adult woman stringently. But not for a lenient decision, that if she betrothed herself, she needs a Jewish bill of divorce for perhaps she was an adult woman. But if her father betrothed her, she also needs a Jewish bill of divorce, lest she was a young woman/נערה, until there will be in her all of these signs of puberty entirely and then she will be considered an adult woman, whether for leniency or for stringency.