I agree, you're not doomed if you can show that you have a strong support system. I'm sure the two of you have thought about how you're going to support yourselves, you probably just haven't documented it.
There are some basic needs your sponsor will be agreeing to seeing to: food, clothing, shelter, medical care not provided by public health services. So, your in-laws will be providing a home, right? As I said, let them write a letter stating so. Your sponsor has in income, it may not be much, but she does have something. What about you, will you be going to school, or anything like that? Get it down on paper. And document your savings too!
If she's just coming to visit, she doesn't need to provide proof of resettling, she hasn't left Canada long-term.