Does she know she's a lesbian?

She probably did know. She had a massive crush on Sheba but she knew nothing could ever happen between them other than a friendship. Still, she could spend as much time as she could with Sheba and in her mind at times she could pretend like they were a couple. She even admitted to it in the end when she told Sheba that she needed more than just a friendship.

She is an old woman who has lived her life basically alone and whatever emotional attachments she can muster are with select female friends. There is definitely latent lesbianism in Barbara but she's someone from an era where she probably never met any out ones in her youth and never fully perhaps understood it was an option for her or even her inclination. Her later diary entries suggest she is becoming conscious her interest is also sexual. She gets into these intense relationships with other women which the other women ultimately find overbearing and break away from. Note Barbara's sister at the Christmas dinner was aware of Jennifer and clearly thought they were a closest couple and when she makes kind of a discreet reference to is (as if signaling to Barbara she is free to talk about her private life to her) Barbara is quite incensed and snaps "I don't know what you mean".

I think no, or if she does she represses it.

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