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"Design! Nonsense, how can you talk so! But it is very likely that he may fall in love with one of them, and therefore you must visit him as soon as he comes." (1.19)
To Mrs. Bennet, "love" is more about proximity than compatibility. Mr. Bingley is "likely" to fall in love with her daughters because (1) he's going to be nearby, and (2) he's rich and single, and they're female and single. With criteria like that, no wonder her marriage is so awful.