@ OP: I agree with the others that say it sounds like your relative is insecure. Maybe she's really been-through something lately----divorce, failed a class, failed at a relationship, didn't get the job she wanted, etc.----or, maybe it's something that she's ALWAYS felt about herself (that she was "less than").
I've had this happen to me ALOT of times, and I've almost always detected insecurity in the person doing it. Another thing that I had to consider, though, was what "I" was doing to contribute to the friction in the relationship. One of the things that I thought about was like someone else said: I was using too many "fancy" words----people don't like it----it makes them feel inferior. Another thing that I came-up-with, that I was doing way-back-when, is that I was particularly using big words with people who intimidated ME----and "I" was the one who was insecure. Also, when I was stating facts, all-the-time, I learned that I was feeling that I was stupid, and wanted to be always giving these facts so that I could convince myself (while convincing others) that I was smart. Oftentimes, I would have GREAT difficulty understanding why anybody wouldn't WANT to learn (because I CRAVED learning in hopes of getting smarter, and learning how to behave, for instance, so that I would be liked)----I would think people would WANT the facts----but people just don't like others pointing it out, to them; so, I just had to keep making myself not do it, until I got it down, pretty good.
Another thing is, females just seem to be more competitive, than males. A good example is watching children play together..... Boys will just hit each other, when they have a disagreement, and they're "over it"----girls will hold "whatever" against each other, 'til kingdom come, for some reason.