I know if I have been exposed to a risk, but do I *know* that my friend has not had unprotected 5ex (not talking about the frend in the OP here, just generally)? Do I know she would definitely disclose this to me? I certainly have no way of being sure a donor from the internet will disclose this to me.
And can I be sure the milk has been collected and stored safely??
No, I can't. The risk might be small, but the consequences are dire. I would not take the risk.