The first time I apply I said that we wanted to establish the common law status with my partner so we can apply for sponsorship visa, that's why I was asking for an extension for 6 months.
The second time I wrote that we will be establishing the common law status soon and we are currently preparing our papers for the sponsorship visa and that we will send them in once we become common-law. I also said that we would be applying outland and that I wanted to be here during the processing. They ask you to provide evidence that you have enough funds to stay here. With that one I also send them a letter from the bank that we have a common account with my partner (that's another evidence that we will become common law). The next day I received approval for 1 more year (that's how long the outland application for me takes to be processed).
In both cases I also showed them copies of my health insurance and I wrote upon approval of my visitor visa I would extend my health insurance policy to cover the whole duration I would be in Canada.
It's important that when you apply for extension that your applications are consistent and that you show that you can support your fiance or she has enough funds to stay and that she has health insurance.
Hope that helps. Good luck