How do we know for which purpose αὐτος is used?

[Smyrnean]

"αἰσθομένη δʼ ὅτι ἀδικεῖσθαι ἔμελλεν ὑπὸ τοῦ Φιλόνεω, μεταπέμπεται, καὶ ἐπειδὴ ἦλθεν, ἔλεξεν αὐτῇ ὅτι καὶ αὐτὴ ἀδικοῖτο ὑπὸ τοῦ πατρὸς τοῦ ἡμετέρου·"

"She said(perosnal ending only) that she herself too was being treated unjustly by our father."

Cambridge Grammar says that this αὐτὴ gives the "she herself" meaning. But how do we know that it isn't just to clarify the subject?How do we know when it gives "he himself, she herself" meaning and when it is merely clarifying the subject? What's the criteria for that?

[mwh]

ἔλεξεν αὐτῇ ὅτι καὶ αὐτὴ ἀδικοῖτο
This exemplifies the two main uses of αὑτός.

(1) ἔλεξεν αὐτῇ “she told her”: “her” unemphatic, just like English unemphatic “her.” Used only in oblique cases, never the nominative.
- Note incidentally that the subject of ἔλεξεν is left implicit: “she” is understood from the context. Greek doesn’t express unemphatic “she” or "he" or "they" in the nominative.

(2) ὅτι καὶ αὐτὴ ἀδικοῖτο “that she herself too was being treated unfairly”: αὐτή “she herself” (as distinct from anyone else). This is how αυτός, -ή, -ό is used in the nominative ("-self").
καὶ αὐτή “she herself too,” the καὶ implying she was not the only one.
- If it were simply ὅτι ἀδικοῖτο, without καὶ αὐτὴ, it would just mean “that she was being treated unfairly,” with no emphasis on “she.”