For me veena and shweta both dislike each other from day 1. They both are good looking, independant , egoistic,control freak females and both love to steal the limelight .
I dont think shweta considers veena as her competitor in any way but she must be definitely upset with veena for insulting her couple of times. I guess the first incident was when veena called manoj to her bed and second was when shweta said "veena sabpe line marati hain" . Shweta does not like anyone bulleying her.
I doubt if veena is jealous of shweta's popularity as ST is mainly TV actress and veena herself is also quite famous.
The main reason they dont get along well is because of their conflicting nature. This is very reason why I feel veena keeps nominating shweta.
Anways, both are good and bad in their own way . Veena is not here to win the game, she jsut wants to get bollywood's attention. I am sure she will be featured in some item song after BB ends. My 2 cents on veena vs sweta !!