It's confusing when you're filling out the form for the first time because it wants you to estimate your monthly income, so everything is based off that estimate, and any difference is made up at tax time. If you don't have a steady income it's hard to know what to put.
In Washington the cutoff for Medicaid/ACA is based on 138% of the Federal Poverty Level, which is $15,060 (X 138%) = $20,782.80, so yearly income below that number and you get shunted to Medicaid, and above you get the ACA. The lower your income above that cutoff, the bigger your ACA subsidy. You can also choose to have all, or none, of your ACA subsidy applied to your monthly premium payment.
Some people estimate their income to land above that $20,782 number in order to stay in the ACA, even if they could qualify for Medicaid. If you estimate your income and it's a little off they are not likely to claw back the subsidy after the fact, because technically you are not eligible for an ACA subsidy if you qualify for Medicaid. To make it more complicated, Medicaid eligibility is based on your monthly income, which is why they ask for your monthly income in the first place. In Washington the max is $1,732/mo. But you can make more than that in one month, just not for two months in a row. So you can stay on Medicaid even if you have a big income event (say, from selling stocks) in any one month, as long as your monthly income is back below the cutoff the next month.
It sounds like your daughter should plan on staying on the ACA if she is likely to get a job soon, as making less than $1,732/mo is unlikely.
She can go to the Healthcare.gov site and report a life change. You can go on too and input different income levels and see what that does to plan cost and deductibles and max out of pocket charges.
Since you have to estimate an income level, it's wise to guess low (within reason) since a lower income in the ACA gets you a lower deductible and max OOP, at least in the Silver plans.
Since she's young and (hopefully) in good health, she might look into a high deductible health plan that is HSA eligible once she starts making more money, if she's not covered by an employer plan, because then she can open an HSA and contribute to that every year for a nice tax break.