I think Mrs Allen doesn't mean to be negligent, she's too simple minded herself to realize what she should have done -- description of her in chap 2 --

"Mrs. Allen was one of that numerous class of females, whose society can raise no other emotion than surprise at there being any men in the world who could like them well enough to marry them. She had neither beauty, genius, accomplishment, nor manner. The air of a gentlewoman, a great deal of quiet, inactive good temper, and a trifling turn of mind were all that could account for her being the choice of a sensible, intelligent man like Mr. Allen."