If your wife is on a six month visit visa, then why does she have to extend? You cannot extend a visit visa beyond six months. The next stage is for you to apply for her residence permit. All you need is to get your six months bank statement (I guess you must have been here for that long). Also, you need a no objection letter from your company, a letter showing you earn up to 5,000 riyals, water/electricity bill, a copy of your passport copy, her passport copy. I think that should be all you need.

I think your company should be handling this stage for you though. I hope this helps.