I don't believe the rebate has anything to do with tax. The option of how you want to claim it does, but not the rebate itself. In that I mean you claim it later to offset your taxable income at tax time kind of like a savings fund I guess for some. For me, I'd rather pay less now. The rebate applies for anyone, paying tax or not if you have PHI, you don't have to prove you are a tax payer to claim the rebate when you take out health insurance.
What a shame for her that she's been paying all this time. Perhaps there is a way to get the money back? I would suggest she ask when she calls her PHI.