It's because of the magic bracelet. It's my theory, but seems lime the bracelet power pierce through a lot of people mind, they don't questioned how weird it was. But since Tatiana's bracelet was broke before, some of the beads even cracked, it almost lost it's power, that's why now most people find Tatiana a bit ridiculous too. And since the beads broke, the power started to reside to another "bracelet" which is MC's bracelet. That's why despite having the bracelet for such a long time (even wearing it at the same day as Tatiana when they first received it), she can't see the system, I think the power can only reside in medium, so if the first is broke, the power will search for another medium.
the bracelet she has have charm magic on it
How can everyone tolerate that girl when she's makit it so obvious they're all dumb to the bone