You have not dealt with this for a lifetime. You’re 21. New therapist.

So I am probably going to ruffle some feathers here but I agree with you that what your sister said, in an attempt to help you and relate to your struggles, was hurtful. Do I think your sister was intentionally trying to be hurtful? Absolutely not. I agree with everyone that she was trying to lessen your hurt by telling you she has not had it easy either and was trying to give you examples of that, but I can see from your point of view where it unintentionally hurt your feelings.
You have obviously been compared to your sister in extremely hurtful ways by those around you. It is absolutely obvious your sister has been told she is special her whole life and has been put on a pedestal by your family, town, etc- although through not fault of her own. Even she seems to be aware of this. You were venting to her about how you have been treated your whole life in comparison to her and she proceeded to essentially say “you will never know what it’s like to be beautiful and smart” and kind of implied because you are neither of those things. “You NEVER have to worry about a professor accusing you of cheating” – because you are not as beautiful as me so people don’t think your stupid like they do me with all my beauty. “You NEVER have to deal with people thinking you slept your way into medical school or are performing sex acts for grades” – because you are not near smart enough to get into medical school in the first place like me and even if you did, you are not beautiful like me so people would never question your intelligence or if you slept with people to get where you are. And so on.
Again, do I think this was what your sister was thinking or trying to imply? No. I think she was trying to be a good sister and help you see that she has problems too. And of course her problems and feelings are valid just as yours, but I can see your point of view on how *her words hurt. You have been told over and over again by those who should support you the most that you are not near as smart, pretty, successful, etc etc than your sister and in your mind, her words just reassured that- unintentionally of course. It is not rationale thinking of course, but human emotions are often not rational.
Her words and the situation kind of remind me of a dear friend of mine. My friend is infertile and could never have children although she and her husband desperately wanted biological children. When she would tell people she could never have children of her own, in an attempt to be helpful, they would say things like “well be glad you cant because children are a handful”, “well at least you can sleep in everyday”, “children are expensive, be glad you can spend your money on whatever you want”. Of course these were people who had the one thing she desperately wanted but could never have. They weren’t trying to hurt her, but to make her feel better by listing to her all their “problems” as a result of parenthood. But really all it did was hurt her more and reminded her of “problems” she would never have. I have a feeling this is how you felt when your sister was trying to explain her hardships to you.

And actually, what is someone with kids supposed to say when someone says, “I can’t have kids and I wish I could?” If you say, yeah, that must be so hard,” you’re acknowledging their pain, but you’re also acknowledging that your situation is better than theirs. So I understand the urge to silver-lining it. If someone said that to me, a child-free person by choice, then it’s easier for me to say, I’m sorry, that must be so painful.

I guess… what else is the sister supposed to say when LW tells her directly that she feels like she has everything? If she’d said, “Yeah, I do have pretty privilege and organic chemistry came naturally,” LW would still feel lesser.

I can think of instances where I was jealous of my sister. Most notably, she moved to NYC to move up in her career around the same time I finished grad school with no job prospects in sight and had to move back in with our parents. I did feel jealous that she’d found her path and was having an absolute blast and I did feel like I was failing, but those feelings were separate. I never felt like she had everything while I had nothing. And I know it’s not the same thing because he never compared us (to our faces), but my dad definitely put down the first job I did nab out of school.

So IDK. I can appreciate that it really must hurt to be compared all the time (and think it’s wild that somehow it’s an entire town of people who don’t know not to make these comments), but I also feel like LW can start taking control of who she spends time with and how she views herself. You’re not lesser, LW, you’re two different people meant for two different paths.

This is sooo inappropriate of your mom.

My brother has major issues I won’t get into, but suffice it to say I have the looks and brains in the family such as they are. Neither of my parents would EVER make any kind of statement comparing us, because why? That would be so wrong. It’s very wrong of your mom too but I almost feel like you and your sister are in somewhat the same league in her mind or why would she even make comparisons.

And yes, people have said to me, often, “that’s your brother? You two look nothing alike.” My dad actually told me confidentially one time that he believed my brother got switched at the hospital because my dad was away when my mom gave birth and she was on heavy drugs and didn’t know what was going on, and she was sharing a room with a literal child who was giving birth probably from incest (New Hampshire, you know, 1972).

Anyhoo. These people are all being assholes and maybe there are things you can learn to say to people to let them know they’re hurting your feelings and should stop it.