[Kaderin Triste]

I mean... I don't guarantee that it's only one raid pass per day, but I only ever have one at a time.
But also, gyms seldom have raid battles occurring at the same time (although I don't know how it is in areas with only a few gyms). But if you get a pass one day and then save it for the next day, you can actually do 2 raid battles by using the raid pass you have, then spinning to get another one after that and using it right away. (I mean, I'm guessing your aunt doesn't visit too often, so it could take some time to get around to using the raid pass if you do the suggested save and use for 2 battles technique, but it could be worth it.)
So even if all three gyms had level 1 raid battles, you could probably only do 2 of them. But really, I don't even do raid battles that often (compared to a lot of people). 1 per week usually depending on my free time, what raid battles (I can only do level 1 and I only need a couple of the pokemon from those) are nearby, and how much battery life my phone has left. And what time of day it is. Late-ish morning to early evening, maybe. Anything between around 9pm to 9am, nope.
And also, depending on your levels, you and your aunt could possibly take down a level 2 raid battle together. (Based on the info that shows after the battle is beaten, I'm guessing you don't even have to be the same team.)