So this story is a few years old at this point, and therefore resolved, however whenever I think back to it, I always feel like I was the only sane one in my family, so I'm going to put this out there and see what the unbiased people of the internet think. 

Relevant backstory:
I was about to start [rigorous graduate degree program] in a state far away from my family just as my sister was graduating from college. She decided to move in with me after graduation with the goal of also preparing to apply for [rigorous graduate degree program] at some point. It is also important to know that the house we would both be living in was purchased as an investment property by our parents (we're very fortunate for all they're able/willing to do for us). We would also be living with a roommate who was one of my classmates, as well as my cat. Finally, it is important to note that while my sister is not a complete train wreck of a human, she is certainly not known for being the most responsible or tidy. 

So right after my sister graduated, she was living at home with my parents for a few months while she prepared to move down to where I was living. During this time she decided that she wanted to get a pet mini pig after meeting a friend's and falling in love. I immediately gave my parents numerous reasons why that was a bad idea:
1. pigs are notorious for being too smart for their own good, i.e. you might have to end up baby proofing your house if you have one
2. no one had any reason to think that my sister was responsible enough to handle a pet pig, and since she planned on moving in with me, the pig would then become my responsibility, which I didn't find fair, especially considering what was going on in my life at the time
3. even though I'm her sister and my parents were our landlords, we also had a paying tenant, who nobody thought to get permission from. In my experience during college, pets were only allowed if all of the roommates consented, and I thought that was still important in this instance. 
4. We didn't know how a pig would potentially get along with my cat, who I had had for over 3 years at that point 
5. My sister was in an inherently transitional point in her life at the time, and was not able to predict where she would likely be in 1, 3, or 5 years, and therefore it seemed irresponsible to get a pet that would likely be very difficult to bring along with her while she figured out her life. 

Despite all of these points, my parents insisted that my sister be allowed to "make her own mistakes". I pointed out that this was ridiculous, because my sister had no money and my parents were planning on bankrolling this "mistake", but that too fell on deaf ears. So, ultimately my sister gets what she wants, a little baby mini pig.

I have to say, the pig was actually adorable and sweet. She got along with my parent's cats and dog well, and was really not too much trouble like I had predicted. HOWEVER it was still not sustainable for a few reasons:
1. pigs can be litter box trained, but you cannot use kitty litter, because they are pigs, and therefore will eat it, and which point it will clump up in their stomach and they could die. Therefore they had to use sawdust, which does fuck all to mask the potent odor of pig waste, and needs to be completely changed out daily. 
2. the pig absolutely refused to walk on asphalt or anything that wasn't smooth. Because of this, her hooves began to grow out of control, and taking her to a vet was not really a viable option due to...
3. her size. She didn't stay "mini" for long. I don't have a final weight, but just know in the short time my family had her, she got pretty freaking big

So as to the resolution for the story, which I suppose isn't as sad as I might have predicted, my sister ended up moving in with me sans pet pig. This was because, as I said from the beginning, the pig was too much work and responsibility for her. This meant my parents (AKA my mom) were now responsible for her. However, due to the overgrown hoof issue, which to my mom's credit, she did try to work on to no avail, they ultimately had to surrender the pig to a farm, which conveniently backs up to their backyard. However she did not stay there permanently, and was eventually moved to some other farm in the area. According to my mom, we would be welcome to visit her whenever we like, but no one has. I don't know what the future holds for this pig though. Will she die of old age on a farm? I find that unlikely, but who knows. 

As for anyone who might be wondering why my parents ever even entertained this idea, I'm still pretty confused about it too, but I think part of it is that my parents have always considered my little sister very sensitive, which is not untrue, however because of this, they tend to treat her with kid gloves. I personally think this has only made the problem worse and kind of stunted her maturity. I would like to note however that I love my sister very much and despite our differences I have considered her my best friend throughout all of this. 

Anyways, thanks to anyone who read all of this! 