All I can say is that if her payment amounts are sent to her monthly, I would have to wonder what type of mortgage company she is dealing with. My mortgage company gives me a payment coupon book for each year. The payment amount might vary slightly year to year based on my escrow payments. My taxes and insurance are escrowed and they do vary from year to year. Since the home values in my are have varied greatly in the last 3 years (way up, then way down) that has impacted my payments. But like I said, they evaluate my escrow account once a year and then issue a new set of coupons based on the new number.
I also bought a 7yr ARM. The idea for me was to get in at a lower rate and then refi when the rates dropped. Guess that little idea worked out pretty good for me. When I bought my house in 2003, the 30yr fixed rate was about 6.5 to 7.0%. I got a 7yr ARM at 5.875%. Just this week, I started the refi paperwork to lock in at 5.75% fixed. I know it could have gone the other way, but I took my chances and it paid off.
So to the OP, if you would like more help, it is likely that we would need more info. It definately sounds strange for sure. I would have to say that if her rate is adjusting monthly, then she probably does not have a conventional mortgage. And, if she defaults on that mortgage, they will simply foreclose on that property and she will only lose that. If she wants to avoid that, she could sell it, even short sell it and avoid the negative credit impact. Even if she has to short sell the property, the bank will forgive the shortage amount and she can walk away.