] Mrs. Allen fails Big Time as a parental figure, doesn't she?

That all depends on what you expect from a guardian. She's no more silly (and much less ill-mannered) than - say - Mrs. Bennet.

] I wonder what Catherine's parents were thinking to entrust their daughter to her care. Surely they knew how vague and spineless she was. Were they counting on Mr. Allen to keep an eye on Catherine?

I thought about this...but then I remembered that the Allens are good neighbors to the Morlands, and they come from a place with fairly limited company. The Morlands are simple people, and I'm sure that knowing the Allens to be honest, decent people was all the assurance they needed. They can be (and rightfully so) confident in Mrs. Allen's true affection for their daughter. As to Mrs. Allen's deficiencies in providing discipline or boundaries, I can only guess that the Morlands either failed to understand the danger that a place like Bath might present...or failed to notice Mrs. Allen's social ineptitude for lack of an example. I doubt Mrs. Morland had many opportunities to observe Mrs. Allen's behavior in a public assembly the size of what her daughter would encounter in Bath.

] But, one thing Mrs. Allen's vacillating does - it forces Catherine to begin to think for herself and reason for herself and depend upon her own judgement as to the "rightness" of an action.

Really? I didn't see it this way. I saw Catherine work things out for herself both in and outside of Mrs. Allen's influence. I'm not sure that I'm prepared to give the silly ol' matron quite so much credit. *grin*