Well, I never applied for law however throughout my time at university I met several law students — they varied from very intelligent to less than mediocre, the thing which united them was the mindset of enjoying working hard.
On a secondary note, I was told by a former teacher of mine that I wouldn’t get into any Russell Group university (kind of imagine UK’s version of the IVY League unis if you’re American) for my degree. I not only proved her wrong, I am currently studying at Cambridge.
Law, in my opinion, isn’t about raw intellect it’s about working hard and rising to meet challenges. People, even your sister, like to view themselves as superior and to imagine no one can do what they do — especially not their younger siblings. It’s only true if you allow it to be. You can choose to accept what she’s said, or you can choose to prove her wrong and not only become a lawyer but be a better lawyer than her. That’s your choice. You either choose to be a loser and be kicked to the curb, or you stand tf up fight for what you know you want either ignoring her or outright not engaging her in the conversation along the way