Single word for 'never return'

I think your best bet is to modify the "gone." For example, "gone for good" or "gone permanently".

Consider abandon

to give up (something) completely or forever: to abandon all hope

Your construction could be She's abandoned us!

Depending on the subjects choice in the matter, I could recommend exile.

(As a verb) Expel and bar (someone) from their native country, typically for political or punitive reasons

If the person leaving was told to go, you could say she was exiled. This implies that she was forced to leave and may not return.

Interesting question. There are quite a few words that you could use to convey the idea of her having left:

deserted, left, quit, defected, for example.

It's much more difficult to find a single word that conveys the ideas of 'leaving' and 'for good'.

Could any of the following work?

Ditched (us), bailed out (on us), cut loose and run, flown the coop, flown the nest (usually used to indicate children having grown up and left home), walked out on.

The best one-word option I can think of is to see if you can think of a famous literary character, and use her name as a verb. For instance, if you were trying to describe a girl who eloped with a lover, you might say she 'Jessica-d' / 'Jessicaed' / 'Jessica'd' as in Merchant of Venice.