Is your daughter currently insured through your employer-sponsored group plan? If so, COBRA may be an option. COBRA applies to employers with 20 or more workers. Coverage lasts 18 months in most cases. She must pay the full premium plus a 2 percent administrative fee. Illinois employers with less than 20 workers are subject to the state's small group continuation law rather than COBRA. Small-group continuation lasts 9 months in most cases.
If your daughter works, she may have acess to her own employer's group health insurance. She has a 30-day window to enroll midterm provided she qualifies to receive group benefits. A human resources manager can provide details.
Explore the individual health insurance market as well. ACA metal plans (bronze, silver, platinum) are available through the Get Covered Illinois Health Insurance Marketplace. Financial assistance may be available if she meets income requirements. A local health insurance agent can discuss cost and coverage specifics for off-marketplace plans. The individual plan should take effect on her 26th birthday, but be in place 60 days in advance to avoid a coverage gap.
Other health insurance options include Medicaid (an entirely income-based program), or a catastrophic individual plan (which does not provide comprehensive coverage).