What I want to know is how the Capitol Police knew the difference between their agents and Ashli Babbitt.

Would they have smoked one of their own at random, or was she a target, or was there a list of "people not to attack because they're actually feds" or was she wearing squibs in her backpack and was in on it the whole time?

They were all feds but also innocent grannies taking a stroll and should not be sent to jail.