Prove it.
First there is nothing that indicates she had any communicable disease. Nothing that I've seen anyway. Perhaps something you saw?
Second, even needlesticks with known infected blood rarely transmit HIV, so yeah, I'd take the bet that a squirt of breast milk isn't going to transmit HIV.
Well, if you are so confident it did not put the officer at risk, you should be able to demonstrate with your person that you can take a squirt of HIV-laden breast milk on your face, without fear.