She is not paying any premium for her insurance, so want to know if claiming her as dependent will result in revoking of her Obamacare insurance
If she receives a 1095-A, it is a "Marketplace" plan. If she receives a 1095-B, it is probably Medicaid.
If she does not have one yet, you may want to contact the insurance provider to find out if it is Medicaid or a Marketplace plan.
If it is a Marketplace plan (1095-A), she can still have insurance, but she will probably need to pay the FULL cost (which can be quite expensive) if you claim her as a dependent.
If it is Medicaid, it may depend on the State, but in many States, it will NOT affect her eligibility for free Medicaid.
Yes, your dependent may lose the Premium Tax Credit for health insurance if you him(her) as depended. In addition, you will have to report that person’s 1095-A in your tax return and may need to repay some or all of any Advance credit the dependent received, depending on your adjusted gross income.
You would need to determine if the amount of savings by claiming the dependent outweigh the benefits of claiming the person on your tax return. See the link below for IRS requirement on subsidy eligibility