Yes. For one thing He could have written in an exception to His law. But it appears that He chose not to do that. Since Mary complied with the law it is reasonable to infer that the birth was of a normal type, and there was blood. We don't have to add anything special to arrive at that conclusion.
I don't think this is at all comparable to Jesus and His baptism. There we are given specific information in scripture, i.e. that He WAS God, such that He did not "need" to be baptized. With Mary, we are given no such information that leads to an exception.
Only if you have no further information. But in this case, we *do* have further information. Therefore, "what is reasonable to infer given the absence of further information" is irrelevant.
-A8