the way I see it, you don't have to have 6 months bank statement as they can see that you haven't been here for that long. why waste money in extending the visa if you can go for RP for her. In my experience both when I wanted to get a house and loans, they ask for 6 months bank statement, but the moment I tell them that I have been her for less than that, they ask you to bring what you have and that usually does it.