Irviniel, be the bigger person. She’s dragging you into girl-drama. She’s already got you doing that thing:
— You downgraded her to girlfriend rather than fiancee to “avoid confusion” (?)
— “she thinks herself a real little expert too…”
— *rolleyes*
— “some woman with a BA…”
— “she this…” and “she that…”
Without speaking to her to get a bigger picture, it’s presenting like EITHER option you presented:
1. She’s trying to score points. You weren’t (originally), but it’s tricking you into a petty girl-fight and you’re falling for it.
or
2. She’s just a little whacky when she learns new things (we all do that sometimes)–and you’re falling into the girl-fight trap here, too.
In fact, I’m changing my advice: Don’t be the bigger woman, because that implies a hierarchy of competitors. Either ignore her or randomly invite her to watch some of the videos with you on this site (as if you just discovered it, not as a confrontation). Instead of fun girl-time taking a Cosmo test, take an ADD test (heh). And maybe if she’s misinterpreting something about you, you can help her understand.
She’s not just a girlfriend–she’s presumably going to be around for a long while–the same as she has to see you.
So just extend yourself in friendship. If it doesn’t work, simply back off and let it go for each of your sanities (she will hopefully come to better understanding of her new knowledge with time).
Best of luck to you! 
ps. Quick story on how us women get into unnecessary drama:
Once my sister was telling me about the most recent guy trouble in her life. I listened and responded, “You know what your problem is, it’s these guys. They’re not right for you.” I said it like a plumber says, “You know what your problem is, lady, it’s these pipes got clogs in ’em. They need cleanin’ out.”
No big deal, right? Well I noticed a subtle look on her face that I steered the conversation away from. Later I found out she was upset because I told her she had problems. “She sat there and told me I was full of problems!”
See how she misunderstood me? There’s what was *actually* said, and then there is what was said put through the drama filters. 