In Ch 17, Mrs. Grant says to her sister:
"But, Mary, do not fancy that Maria Bertram cares for Henry. I am sure Julia does not, or she would not have flirted as she did last night with Mr. Yates; and though he and Maria are very good friends, I think she likes Sotherton too well to be inconstant.”
But Mrs. Grant is wrong, back in Ch 6:
turning to Miss Bertram particularly as he [Mr. Rushworth] spoke. But Miss Bertram thought it most becoming to reply— “The avenue! Oh! I do not recollect it. I really know very little of Sotherton.”
Later in Ch 8:
Miss Bertram could now speak with decided information of what she had known nothing about when Mr. Rushworth had asked her opinion; and her spirits were in as happy a flutter as vanity and pride could furnish, when they drove up to the spacious stone steps before the principal entrance.
Maria does not like Sotherton well enough to be constant. When Henry is listening at dinner, she pretends to know nothing of it: her attachment to Sotherton is not strong enough to overcome her admiration for Henry. Only when she is snubbed by Henry (Julia is sitting with him), does Sotherton have value to her. Only when Henry leaves for Bath doe she decide to marry Rushworth.
Her commitment was never strong enough.
