The Bunner Sisters - The Proposal

I was shocked when Mr. Ramy proposed to Ann Eliza. Yet, what surprised me most about the event was Ann Eliza's reaction, especially after he left. On page 316, Wharton writes: "She felt unutterably thankful to be alone. She knew the crucial moment of her life had passed, and she was glad that she had not fallen below her own ideals. It was a wonderful experience; and in spite of the tears on her cheeks she was not sorry to have known it". She goes on to say that Ann Eliza regretted that it happened in the shop and that she was not wearing her black silk. I was confused upon reading this, as I wonder how Ann Eliza felt about Mr. Ramy. I understand that she probably didn't think she could marry him because she knew how Evelina felt too, and that she gives priority to her sister's feelings. Yet, to me, this passage seems to make me think that Ann Eliza simply has a rule that she cannot marry, as she says she is clad she "had not fallen below her own ideals". Did she reject Mr. Ramy simply because she feels that she cannot or should not marry? It seems that she feels she must be a sacrifice in someway - that her following her heart cannot be. I suppose she is simply glad to have been proposed to, as Wharton later writes of how "no impoverishment could rob it" (317). I was just a little surprised by this entire exchange and Ann Eliza's feelings afterward.