Elizabeth is a very stable person. However, twice now she has had replicator nanites induce psychotic hallucinations. The first time she spent what she perceived at the time as nearly a year trapped in her own mind, living out a false reality without Stargates--living in and out of asylums, and suffering twisted hallucinations of what was occurring in reality.

The second, just before she arrived on the island, was much more brutal--like the worst fever nightmares imaginable. Twisting, ever-shifting cascades of false realities and terrors that would severely strain the sanity of anyone subjected to it.

She's fairly stable on the island, but she did spend a week denying its reality--and occasionally doubts it even now. The experience did take a toll on her psyche, but it's up to Del as to whether mechanically induced hallucinations are under Delirium's domain or not.