Fanny is at least fifteen years old when she goes to Southerton, her first real trip of any distance. It is ten miles and quickly she is beyond any distance she has been previously. "Their road was through a pleasant country; and Fanny, whose rides had never been extensive, was soon beyond her knowledge, and was very happy in observing all that was new, and admiring all that was pretty."
I think it is disgraceful that Fanny has not been included in activities before now. She is treated little more than a glorified servant, imo. Even the servants are probably getting time off now and again to do things they want to do. Lady Bertram's insistence that she can not do without Fanny should have been overridden by someone before now. There are others in the household, including Mrs. Norris, (if Sir Thomas had ever insisted, she would have had to relent) who can take over in Fanny's place now and then long enough for Fanny to get some time away to enjoy herself for such activities.
I know, I know....there are many reasons one could come up with to explain the situation but they will be reasons for excusing all the family members for their negligence. She's been there for at least five years. I realize she is not 'out' yet, but surely, something could have been done on her behalf before now.