I did originally post this as a comment but I may as well post it here as an answer to the question. Its short and not very well thought out, but here it is:
I know it just seems like a silly, immature topic, but I think it's fairly valid. Charlotte doesn't place a lot of value on marriage, and gets married to Mr Collins as just a means to get a stable life. She, unlike the other girls in the book, did not even consider that marriage should be for love, and was willing to put up with a completely insufferable man. Conversely, she was devoted to Elizabeth, and loved her in a way she would never love her husband. At the time, homosexuality would have been abhorred, so if she was romantically inclined towards her friend, she would have had to suppress it. However, Austen was, in her own way, a feminist, even though she has a bad reputation for writing novels centred around marriage. It wouldn't seem out of place at all for a lesbian to feature in her books, even if it was subtle, an in joke of sorts. Opinions?