] The 'scarcely ever prevailed on to get out' suggests that she was rarely asked in - though it might have appeared that Charlotte would not want to inconvenience Anne by inviting her in, I feel it also hints that she didn't invite her because she wasn't interested in her company :).
According to my dictionaries "prevail on" has the meaning of being persuaded or coaxed into doing something. To me that meaning implies that Charlotte tries very hard to invite Anne but Anne seldom let herself being talked into a visit inside the parsonage.