i think everyone took kavita's statement too literally. may be she wished even prayed that vedika go mad to ensure ant's married life.....however when vedika went really mad and dhruv became paralysed....she bagan to feel guilty and blamed herself for making it happen by wishing for it (and god granted her wish). in any case i never thought kavita was the culprit, she is too kind to do something like that even if she is partial to ant.
now for ant .....though i doubt it but he could be the culprit ,however his motives may not be entirely selfish. i doubt he knows about niharika's infidelity or would drag his sister through all this. he may be spoilt a little but he is not stonehearted and disloyal to his family. for most part he is shown to be an emotionally needy but mature and simplehearted person. as for the motive if he was indeed responsible for vedika's insanity....he was the only person who knew about dhruv's sacrifice of his love before the marraige and was not bounded by any promises.he could have refused to marry nih and ensured that dhruv gets his love , instead he let the nupital go ahead and let dhruv make the sacrifice.he must have felt terribly selfish and guilty.since he does not know about dhruv rejecting his ex in favour of vedika or the vedika-dhruv-suraj fiasco...he assumed that dhruv is bearing vedika's burden unwantedly being the responsible person he is. so ant set out to correct the wrong in his own misguided way. he decided if vedika goes crazy without any hope of getting better, sooner or later dhruv can divorce her and get on with his life , maybe even his love(and he will be justified in doing that). what he misunderstood was the depth of dhruv's feelings for vedika and vice versa.