Here are Charlotte's own words on the subject:
"I am not romantic, you know. I never was. I ask only a comfortable home; and considering Mr. Collins's character, connections, and situation in life, I am convinced that my chance of happiness with him is as fair as most people can boast on entering the marriage state.''
Charlotte insists that she does not wish to marry for love, but only for security. She intimated this earlier in the book when she advises Elizabeth about Jane:
"Happiness in marriage is entirely a matter of chance. If the dispositions of the parties are ever so well known to each other, or ever so similar before-hand, it does not advance their felicity in the least. They always contrive to grow sufficiently unlike afterwards to have their share of vexation; and it is better to know as little as possible of the defects of the person with whom you are to pass your life.''
Charlotte agrees to marry Mr. Collins for security and to avoid remaining an "old maid." Although her friend, Elizabeth, refused Mr. Collins' proposal, Charlotte decided to marry him when he asked her.
The times being what they were, it was difficult for a woman to remain unmarried. She was dependent on her father, then on any brothers, to support her until she found a husband who would take over that duty. Sounds pretty amazing from our 21st-century perspective, and yet, that's how it was. Charlotte, fortunately, is patient enough to endure Mr. Collins' less than desirable personality traits, specifically the way he sucks up to Lady Catherine de Bourgh, and so feels that she made a very good match.
Check the link below for more information on all of the characters from this book. Good luck!
Lizzy wonders the same thing, and her sister Jane answers her:
You do not make allowance enough for difference of situation and temper. Consider Mr. Collins's respectability, and Charlotte's steady, prudent character. Remember that she is one of a large family; that as to fortune, it is a most eligible match; and be ready to believe, for everybody's sake, that she may feel something like regard and esteem for our cousin.
In other words, Charlottle is not like Lizzy or Jane. She may think that Mr. Collins is a very good match for her and that she may even have some affection for him. Remember that since the Bennetts don't have any sons, Mr. Collins will inherit their house and land when Mr. Bennett dies.
Charlotte, who is in her mid-to-late twenties, is already an "old maid" by the standards of her day. She points out that she is not as fair as many of her friends; in addition, she has not received other offers of marriage. If she stays with her parents, she will be both an emotional burden and a financial strain. Charlotte is a practical woman. She recognizes Mr. Collins as a man who, while not without personality quirks, will provide her with a safe home and security. Charlotte considers the proposal to be the best deal she's going to get, and she acts on it.
Intelligence and acceptance of fact:
Charlotte, whilst not exactly an "ugly-duckling" has reached twenty -seven without a marriage proposal or any obvious (in the story) male interest in her. She seems prepared to accept a loveless attachment as long as her future security is guaranteed. Mr Collins, although made cumbersome, awkward, boring and self-effacing in the story, is but twenty five years old and his future is doubly secured by his parish and his future ownership of Longbourn by entailment. She, to coin a phrase, jumps in "where angels fear to tread" and siezes a golden opportunity that may not come her way again.
She is quite open in her explanation to Elizabeth of her actions and, although the Reverend gentleman seems to have got the better of the bargain in terms of an ideal suitor, Charlotte may well be recognised as just a sensible young lady who acts wisely in the face of adversity and wins a personal battle. Well done Charlotte from me.
Charlotte Lucas has nothing to offer a husband except herself. She is from a family formerly in trade with very little money to bring to the marriage. Her "conections" or relatives are not gentry, and she herself "has never been handsome" and at 27 has gone beyond the usual age for marrying. She is very intelligent but we do not hear of her "accomplishments" such as singing, speaking romance languages, designing ornaments - which along with beauty are used to attract men. In short, she is at the end of her rope. She can't work without literal degradation (i.e. de-grading by becoming a governess) and will have to live on the kindness of more fortunate members of her sibblings, if there are any. In this situation marriage is "the pleasantest preservative from want" no matter how unsuitable the husband. Elizabeth and Jane want to marry for love, and Elizabeth is shocked to find Charlotte marrying for money, but as Jane notes, she has little choice, and in finding Mr. Collins , Charlotte "feels all the luck of it."