Captain Buckler had seen things very differently the morning after Neil's recovery. She didn't go into details, but the Captain saw The Unknown Alicorn Male as a threat to be contained. Calling him a wildcard and a possible threat that needed to be thoroughly assessed before he was given access to the castle. Why she thought that when all he did was run from the guard, he didn't know. Either way, she denied his request to join Neil's guard detail.