While Mrs. Norris had no children of her own, I think we get a glimpse of her parenting style with Maria and Julia in Ch. 2.

...they thought her prodigiously stupid, and for the first two or three weeks were continually bringing some fresh report of it into the drawing–room. “Dear mama, only think, my cousin cannot put the map of Europe together—...

and yet it is Mrs Norris who answers them

I'll only quote her counsels not the girls' complaints about Fanny
“Very true indeed, my dears, but you are blessed with wonderful memories, and your poor cousin has probably none at all. There is a vast deal of difference in memories, as well as in everything else, and therefore you must make allowance for your cousin, and pity her deficiency. And remember that, if you are ever so forward and clever yourselves, you should always be modest; for, much as you know already, there is a great deal more for you to learn.”...

“To be sure, my dear, that is very stupid indeed, and shows a great want of genius and emulation. But, all things considered, I do not know whether it is not as well that it should be so, for, though you know (owing to me) your papa and mama are so good as to bring her up with you, it is not at all necessary that she should be as accomplished as you are;—on the contrary, it is much more desirable that there should be a difference.”

Such were the counsels by which Mrs. Norris assisted to form her nieces’ minds; and it is not very wonderful that, with all their promising talents and early information, they should be entirely deficient in the less common acquirements of self–knowledge, generosity and humility.

Lady Bertram was a busy woman. I love how Austen describes her.

To the education of her daughters Lady Bertram paid not the smallest attention. She had not time for such cares. She was a woman who spent her days in sitting, nicely dressed, on a sofa, doing some long piece of needlework, of little use and no beauty, thinking more of her pug than her children, but very indulgent to the latter when it did not put herself to inconvenience, ...Had she possessed greater leisure for the service of her girls, she would probably have supposed it unnecessary, for they were under the care of a governess, with proper masters, and could want nothing more.

In Ch.4 also, we're told
Mrs. Norris, in promoting gaieties for her nieces, assisting their toilets, displaying their accomplishments, and looking about for their future husbands,...

Lady Bertram did not go into public with her daughters. She was too indolent even to accept a mother’s gratification in witnessing their success and enjoyment at the expense of any personal trouble, and the charge was made over to her sister, who desired nothing better than a post of such honourable representation

I think the reader is being told that doting Mrs. Norris eased herself into the mothering role of the girls, assuring the girls on the one hand wonderful they were to the point of vanity, and almost to think meanly of others (or at least Fanny) a la Mr. Darcy's upbringing.