Chuse properly, chuse a gentlewoman for my sake; and for your own, let her be an active, useful sort of person, not brought up high, but able to make a small income go a good way. This is my advice. Find such a woman as soon as you can, bring her to Hunsford, and I will visit her.' (Chapter 19)

Mr. Collins’ proposal to Lizzy is hilarious because he hears nothing that she says, transforming her refusals into compliments or amiable reluctance or an effort to increase his affection by suspense. LoL! However Mr. Collins does not have much respect for Lizzy anyway. At the Netherfield ball in Chapter 18 he refused to listen to her advice not to approach Darcy to which he replies: My dear Miss Elizabeth, I have the highest opinion in the world of your excellent judgment in all matters within the scope of your understanding which I think is rather derogatory of Lizzy’s judgment. His opinion of Lady Catherine is very different. He is all too often eloquent in her praise so I have to wonder why he does such a poor job in following her advice by proposing to Lizzy. He must be blinded by Lizzy’s beauty and amiable countenance. To break it down:

Chuse properly, chuse a gentlewoman for my sake; and for your own,

Lizzy is the daughter of a gentleman; so far so good.

…let her be an active, useful sort of person

Lizzy is active, she is a good walker and a fabulous companion from what I have seen but is she useful in the way that Catherine means. I think Lady Catherine means his wife should be used to doing some domestic chores herself. I do not see any evidence that Lizzy does these sort of domestic duties.

…not brought up high,

Lizzy is probably brought up too high according to Lady Catherine’s criteria; she does not have anything to do with the kitchen (Chapter 13) and certainly does not help with mince pies (Chapter 9) other than perhaps ingesting, as they have servants to do their work at Longbourn.

…but able to make a small income go a good way.

Lizzy does not seem to be a spendthrift but the only evidence of frugalness is that Lizzy is trimming a hat in Chapter 2. I take it that she is renovating a hat rather than buying a new one. I wonder if she prefers fruit to flowers. I agree with JA that is seems more natural for flowers to grow out of the head!

Does Charlotte know of Lady Catherine’s advice? I do not suppose she does but she seems to be the embodiment of it. Charlotte's practicality and providence meet up when she decides to reel in Mr. Collins. She is doing him a good deed as much as herself by doing so.

Chuse properly, chuse a gentlewoman for my sake; and for your own,

Charlotte is the daughter of a gentleman; as before, so far so good.

…let her be an active, useful sort of person

Charlotte, IMO, is exactly the kind of lady to which Lady Catherine refers. She has been brought up to help in the kitchen as Mrs. Bennet’s description of being wanted about the mince pies in Chapter 9 suggests.

…not brought up high,

Charlotte is the daughter of a newly made gentleman and combined with her practical domestic experience is evidence enough for me to believe she was not brought up too high for Mr. Collins. In Chapter 13 Mrs. Bennet says “I hope my dinners are good enough for her. I do not believe she often sees such at home.” I think Mrs. Bennet is stating a fact although it is rather unkind of her to mention it.

…but able to make a small income go a good way.

Charlotte has been raised in a large family that has not enough servants to do the work which to me indicates they have a smaller income than the Bennets. Jane describes Charlotte as “prudent” to Lizzy in Chapter 24, " Consider Mr. Collins's respectability, and Charlotte's prudent, steady character.” I also think since her mother did train her in the kitchen she has probably also trained her how to make an income go a good way.