With feminine-them אִיתָן.
Firm, strong etc - אֵיתָן. It is also the source of the Biblical name איתן (Ethan).
DL Hebrew reminds me of the Israeli tv program סרוגים insofar as the sentences relate ideas that make sense in Israel where the orthodox separate men and women. In this sentence, the female reads books with other women, not with men, which would be איתם. Not a critique of DL or Israeli culture & I don't assume DL has a stated position on such matters. At any rate, it makes sense to introduce us to phrases that one could easily encounter in Israel.