Can’t Work Due to Health, Will I Lose Coverage?

My girlfriend has marginal income. I think she made $19K last year. She purchased a marketplace healthcare insurance plan at beginning of 2014. In Dec, 2014, she had to have major spinal surgery. Also, in December, she chose the same healthcare plan for 2015 as she had in 2014.

She is still recovering and unable to work. I think she can start working again in April.

As a waitress, she will need to apply for a new job and be hired before income begins to flow again. So I understand that there is a minimum income requirement to qualify for marketplace insurance.

She has ongoing health concerns and would like to keep her current insurance, but obviously she cannot afford the premiums without the healthcare insurance premium tax credit.

My questions are:

1) what does she use as income justification for her insurance company (required by end of March) to continue receiving the monthly premium tax credit payment advance, and

2) once she is working again, what if she makes less this year than the minimum income requirement?

Will she be billed by her insurance company for the remaining premium for the whole year? That would be a bill of around $4300! Thanks for any advice.