I suggest starting with its clinical term (depersonalization/derealization) - she should be familiar. Unless you're unsure if this is what you're experiencing and want to describe it to find out? When talking to non-medical professionals I say things like:

- living behind glass
- the world looks/feels like I'm watching a movie of it
- I look down at my hands and I don't feel they belong to me (like looking at objects)
- nothing feels real, like it's an illusion but I'm the only one left 'outside' of it
- feeling existentially alienated, estranged