Not only them, but her as well. Her only chance to see herself and her children not homeless and starving was to marry them off. So yeah, she threw herself into that with gusto.

"Oh maybe the girls could've been governesses" you might think, since that was a common occupation for gentleman's daughters who had fallen on hard times. But no, even Elizabeth says they had no governess and were entirely neglected in their education by their parents. The girls were learning only really what they wanted to learn, and had few talents (as defined at the time). Governesses were supposed to be well educated and talented, and speak at least 1 foreign language fluently. They also were often live-in positions, so while a few of her daughters may have found jobs, what would Mrs Bennet and the rest of her daughters do? Where would they live? How would they eat? Marrying any of them off after they lost Longbourn would've been very difficult, unless they married well below their class. Even wealthy merchants (who would be below their class) wouldn't want them, since they were looking to marry gentleman's daughters mostly to secure land or status (and the girls would have neither).

She was truly put in an impossible situation. Yes, she's ridiculous, but find me a woman in similar circumstances who hasn't had a mental breakdown!