I have been pondering a bit about this over the weekend, but felt like I wanted to hear about other peoples opinion for insight

So ever since I (23 years old) recently got my driver licence, I have been driving my sister (15) around to her friends and family cottage as it is too far for her to walk to those places. That I am fine with as long as it is asked about instead of just being suddenly sprung on me, which usually doesn't happen. But the other day I got a bit annoyed when I was going to pick her up after her friends birthday party.

I was asked the day before if I could drive my mom to the cottage, and take back the car since it's battery has been having issues with the cold here and dying on her, so she wanted it in a safe place, and if I later could both drive my sister and our cousin to the party, pick her up around the time it was done, get her and drive her to the family cottage. I accepted and said fine, I can do that as it's the least I can do to have the house to myself, and it's only a 10-15 min drive each way. 

Next day comes and I have had a long day at work and are a bit exhausted, but can't really take a nap as I have the drives I need to do. When they come home, my sister asks if I also could drive her to her cousins house an hour before the party, a house which is a 2 minute drive. I say fine and decide to do that after driving my mom. when returning, I tell her to get ready to be picked up, and I have to wait 5 minutes until she actually get's in the car after arriving home and drive her over, an hour pass, I drive to our cousins place, pick them up and drive them to the party, and I say I will call when I am on my way and they need to get ready.

time passes again and I go to pick them up, I get a message from my cousin that my sisters phone has run out of battery (which is a common occurrence much to our dismay when trying to contact her) and tells me to tell her when I'm nearby. I do so about 2 minutes before I get there so they have time to change to cottage clothing, and get the message to wait a few minutes. After 5 minutes passed after the appointed time, I send a new message to my cousin "Are you guys ready soon?" as to which I get no responses. Another 5 minutes pass until I finally see them walking to the car. A bit annoyed I tell them to hurry up so that we could go. After driving for a little bit and my sister does a bit of small talk and I respond, albeit not the best of moods, which makes her go "Why are you mad?"

For context, this is a sentence I hear so often from her that it actually drives me mad. My sister loves small talk too much, while I in general are a very reclusive person. Which tends to make me a bit annoyed when she talks for way too long. and that usually prompt her to ask me that. it has gotten to the point where even me and my parents have to tell her to stop saying it since just because people aren't "happy" they aren't necessarily "mad", and then she get's a little offended when we get annoyed because "she was just asking". 

So prompting that question, I frankly just responded "because you two spend a lot of time when we had an appointed time, and didn't tell me when you where done, while also leaving me in the dark about when you where done", where she argues that the party didn't end until I arrived and they had to spend the 10 minutes getting ready, which actually means they are taking their sweet time, and that I have no reason to being annoyed/mad. Me just wanting to get home again, drove the rest of the ride quietly, left them off where they needed to be, and went home

TL;DR Had to drive my sister to and from a party, had an appointed time that they overstayed, did not clarify when they started getting ready, which prompted me getting annoyed, and telling my displeasure when she questioned it. AITA?