Bradskii is bound determined not to look at his mistake, so for the sake of completeness I will just finish the argument without him:
(I assume that if she already had the ability to discern whether the rule is reasonable, and therefore already knows not to swim in the dangerous surf, that you wouldn't need to give her the rule in the first place. After all, why give her a rule to do something that she already knows not to do?)
A rule is not a suggestion. A rule and a suggestion are two different things, and a person who gives or receives a rule is not giving or receiving a suggestion. A rule (or prohibition) is binding in a way that a suggestion is not.
So say she breaks your rule and swims in the dangerous surf. I assume you would fault her for this and decide whether to punish her. Would you fault her primarily because:
A) She did not recognize that the rule was reasonable, or
B) She did not listen to you
Bradskii has implied that rules should be treated as suggestions, and that one should act in accordance with the rule if they agree with the rule, and ignore the rule if they do not. This is essentially to act as if the rule did not exist. Now suppose Bradskii's daughter follows his advice and treats his rule as a suggestion. In that case she has not done anything wrong in breaking the rule; she was merely offered some advice which she declined. This is obviously incorrect.
Secondly, if she has only to assess the rule itself, then Bradskii must answer with (A) instead of (B), which is also incorrect. As noted, if she is just going to subordinate the rule to her own lights—as Bradskii proposes—then there is really no reason to give her a rule in the first place. After all, no one gives a rule and then instructs that rules are to be treated as if they do not exist (or as if they have no binding force, and can be overridden at will).
So when Bradskii construes Christian moral laws as, "Act accordingly if you agree; ignore it if you disagree. That's all you're doing anyway," he is not even being consistent with his own experience with his children. He would never tell his child, "Obey my rule if you agree; ignore it if you disagree." The key oversight on Bradskii's part is the authority and provision of the lawgiver. The correct answer to the question above is therefore, "B) She did not listen to you." The lawgiver gives a binding law on his authority in order to help the person bound by the law, and this is what the parent is doing who sets rules for their children. If the children were competent to decide for themselves they wouldn't need rules. The only reason they are given a rule is because they are not competent to decide for themselves. And the key and meritorious act of the child is trust in their parent, not a rational assessment of the rules they have been given.
Finally, Bradskii wants to say that a decision about whether to follow a rule is always made by the individual. He is emphatic that it is the individual who gets to decide. But this is a non-starter and a preoccupation of classical liberalism, for the real essence of rule-following is trust and
auctoritas. The decision is not even primarily about whether to follow a law. It is about whether to trust and abide by the lawgiver.