I agree with everything you say, however, I think that Anne now marrying Charles is more than Anne being able to withstand LR's influence.

Even at the age of 19, Anne was level headed and sensible, so she wanted to make a prudent choice in marriage. At the age of 22, prudence was still presumably of importance, but not as the only consideration. I think that Anne was persuaded by LR the first time because following that particular advice would fit with her general character. Marrying merely for prudence was not something that Anne felt comfortable with, and so could not be persuaded, even if she did look up to LR's advice