you report the 1095-a info on your return. whether you have to pay back the credits will depend on household income which in your case is yours since you say she has none. form 8962
did you have minimum essential coverage during 2018 because, there will be a penalty if you are not covered
the issue for not claiming her is that without any income she should not be covered by the marketplace but by your state's medicaid.
for 2018, since she received ptc she would have to file her own return.
your filing status claiming her would be head of household
without her single.