It is not a case of "never having ventured". It is a case of staying in Hartfield with her father, who can problaby rarely be persuaded to let her go away. Mrs W says she goes very seldom from home... and I thnk we can imagine she sometimes visits Isabella in London...
She is saying that a single woman with a small fortune is considered in society a figure of fun, especially if she is alos foolish and has no ohter way such as a sharp tongue or quick wits, to help her compel some respect.
Miss Bates is however loved, albeit not respected, becuase she is good humoured and warm hearted...