Vishal is using Teja not the other way. Vishal and Nishant always do fun skits with Teja probably b/c they know it might get them some footage. Check the live feed Vishal is in almost every single shot Teja is in. Even if she is with Simba he stands in corner and just watches. It's creepy. Also, I don't think she is using Karan either, they both are real good friends outside and she couldnt feel that connect anymore so she trying to have maintain their friendship. Also, that house is a luxurious prison so probably the fact they she knows him from before might be an other reason she might be looking close to him.
Also it's very unfair to judge someone cause of other actresses that might share a bit of similar personality. Teja is her own person and she should judged for her own personality and not every cute/bubbly person is not opportunitistic. I understand you don't mean it in a negative way and its a just curious post. She might be opportunitistic she might not be. Its honestly too early to say anything. So we all should just sit back and relax and watch their personalities unravel which they will very soon 😄