Fanny dined at the parsonage before the Crawfords came to MP:

“But now I must be satisfied about Miss Price. Does she go to balls? Does she dine out every where, as well as at my sister’s?”

“No,” replied Edmund; “I do not think she has ever been to a ball. My mother seldom goes into company herself, and dines nowhere but with Mrs. Grant, and Fanny stays at home with her.” (5)

It seems Edmund has never thought before of Fanny visiting but Mary’s questions alert his mind to it and he sees that she is invited and then allowed to visit Sotherton. Of course a day visit to Sotherton, the future home of her cousin, is not society. I suspect Fanny’s lack of visiting was probably due to Lady Bertram’s indolence—did she ever go anywhere but the parsonage? Fanny turned eighteen the July before Sir Thomas returns from Antigua:

Such was the state of affairs in the month of July; and Fanny had just reached her eighteenth year, when the society of the village received an addition in the brother and sister of Mrs. Grant, a Mr. and Miss Crawford, the children of her mother by a second marriage. (4)

Is it really derelict that Fanny was not out in society at seventeen years of age? Julia is two years older than Fanny and I don’t think her or Maria was out at that age. At eighteen Fanny has a coming out ball at home which is more than her cousins had, most likely due to a lack of finances:

And her thoughts flew to those absent cousins with most unfeigned and truly tender regret, that they were not at home to take their own place in the room, and have their share of a pleasure which would have been so very delightful to them. So often as she had heard them wish for a ball at home as the greatest of all felicities! And to have them away when it was given… (28)