AITA for becoming hysterical at a school secretary's expense?

Throwaway- Im just going to get in to it.

I (19M) got a call from my mother frantically telling me that she got a call from my sister's school because apparently she had ingested peanuts, she is deathly anaphylactic, I was at home for reading week, and am studying for upcoming midterms, but dropped everything and drove as legally fast as possible to get down to the school.

I ran in to the the office which was really crowded. There was only one secretary, and I knew instantly who it was- My mother and alot of other parents complain about her being a short-tempered smart ass.

I ran in but there was a line up, I told her my urgent need to talk to her right now due to my sisters allergic reaction and she looked at me and asked if I was blind "there's a line hun".

I waited for about 2 minutes before telling her this really cant wait, she put up a finger and picked up the phone.

I got upset and she called a hall monitor to escort me outside the office until she was "Ready to talk to me" I was yelling to tell her about my sister's allergic reaction yet she told me she didn't want to hear it. I was in absolute awe at her attitude, especially with the situation I was in.

I dialed 911 because it seemed like the school didn't give any fucks about my sister. The secretary saw me and ran out to to tell me to hang up.

She started by telling me "See hun, I told you to wait for a reason- there was a mix up, A student told your sister that she gave her something w/ peanuts as a joke, we are dealing w/ that student right now, I could have handled this situation a lot better- I have a lot of students to deal with"

I looked at her and said "what on earth are you talking about, my sister is deathly allergic and you expect me not to be worried and to wait and do nothing? Every fucking second counts in an emergency you fucking idiot, what were you expecting? Were you waiting to keep me on edge for as long as possible before telling me?"

I yelled at her for a bit more and she started to tear up and walked off, the monitor told me to leave "The school isn't going to deal with a hysterical child, we are waiting for your parents, where we will then deal with your attitude"

Are you serious? How am I supposed to react in that situation? Yes, I agree I was really angry, but I feel like I was justified- My sister could have fucking died, all she had to say was there was a mix up- I would have waited if I heard a logical reason like that as to why she didn't need to talk to me right at that moment. AITA?

EDIT-

To add context, some people are confused as to why I didn't immediately go to the hospital, the reasons why are because

1.) I don't know what hospital to go to

2.) they were not contacting me, even though im on her emergency contact

3.) from my understanding, she ran to a teacher and told her she was going to have an allergic reaction, so she got sent to the nurse and my mom was notified, before anything went down the idiotic student who tricked her, told the teacher that it was a "prank" and that she didn't actually have any peanuts, obviously it was a really dumb and small prank that turned in to a big situation, I guess the faculty themselves were confused about what was actually going on so they were unsure what to actually do.