I cant beat Elesa in Pokemon White?

The problem with your pokemon team is that dewott, togetic, archen and feebas are weak to electric type pokemon already. You should try using a ground-type pokemon, because it has no effect on electric. I would suggest maybe a seismetoad, or another ground type. Elesa has 2 Emolga and 1 Zebstrika, so Ice and Rock type moves are good on the Emolga, and ground is good for Zebstrika. If you don't have a pokemon that has a ground type move, teach it a TM, like Dig, or Rock Tomb. and also, i would recommend you have lvl 30 pokemon for the battle.