This is state-dependent. Maryland looks like a weird one in that full educational rights for students with disabilities do NOT automatically transfer except under specific circumstances. In other states it would be automatic and the school team would need your child's permission to even invite you to the meeting.

And IEPs are K-12, public schools only.

At 18, student is their own educational decision maker, even if you don't approve of their decisions.

IME, kid was required to be permitted to attend IEP. Parents could not prevent attendance - not that I wanted to do that. Kid is one member of the team. But so is parent. So decisions can be made that parent doesn’t like.

What does the IEP conversation look like after children turn 18? Can a school "counsel" a young adult into changes to her classes against parent wishes, if the child consents? Even if there is no disability related to the specific class they are counseling her about? (DD has profound anxiety and depression, making her likely to acquiesce to ideas that go against her needs)