Any Rand believed that the US was the greatest country where individual rights were sacred. She denounced the initiation of physical force against the individual as immoral and illegal. In the US it is still legal and acceptable for a parent to use physical force to discipline their child. How is this not a moral and legal contradiction?
Rand is making a comparative judgement. If corporal punishment is practised in the US, this by her own standards is a defect in the US recognition of individual rights as sacred since it involves physical force against the individual and she disapproves of that. But other countries may be more defective - violate more rights more drastically. The US could - just could - be the greatest country where human rights are sacred in the sense that it has the best record. That doesn't imply - and nor need she - that the US is perfect in its respect for individual rights. If corporal punishment is a blot on the US's rights-respecting record, the US's record may still be the best. So Rand is not necessarily caught in a contradiction, legal or moral.
This is not to defend her position. It is just to indicate how she could coherently make her claim - support her belief - about the rights-respecting pre-eminence of the US despite its ongoing use of corporal punishment.