She has gone, means that she is no longer at a particular location.(She has gone to work.)

She has left, means essentially the same thing. (She has left the house to go to work.)

She IS gone, is more of an interjection. It shows surprise. (Oh my goodness, she is gone!) as an example. It could be ;permanent as in leaving a job or in a divorce, but does not have to be.

When I was first learning English as a boy, this sort of stuff was very distracting! But as we grow WITH English, we learn the subtle differences.For a beginner, it really does not matter.

She has gone =  She has left

This tells us what the person has just done.

The main verb is go, and the tense is present perfect: 'have' is the auxiliary verb and 'gone' is the past participle.

She is gone =  She is not here

This tells us that the person is not here any more. It has an air of finality about it, suggesting that the person has disappeared, been fired from a company, or ( a very common) usage, that the person is dead. For example, "Will you remember me when I'm gone?" is a question someone might ask about a time when they are no longer alive.

The main verb is be, and the tense is present. 'Gone' is a subject complement. You could think of it as a predicative adjective ( like 'drunk', for example).  Another way of seeing 'gone' like a kind of adverb, similar to 'She is there', 'She is upstairs', 'She is home' or  'She is abroad'. It tells us where she is.

NB  I think that unusual constructions such as 'She is gone' or 'My keys are gone!' may be a relic of a time when the verb 'to be' could be used as an auxiliary for perfect tenses. Most other European languages have a composed tense where changes of location or state (go, come, disappear, die) take the auxiliary 'to be' as opposed to the more usual 'to have'.  I suspect that this was the case in English, too, at some point in the past.

The past participle of verbs is often used as adjectives.

For example, "He is interested.  He is tired.  He is retired."

In this example, "He is gone", gone is acting as an adjective meaning that He is (not here) or He is (no longer here).

She has gone is the present perfect tense (present tense of "have" + past participle of the verb "gone")

They are more or less interchangeable, but you would rarely use "She has gone" all on its own. You would stay "She has gone to the store", "she has gone upstairs to do the laundry." You are referring to a past action with a simple result. It's equivalent to "she went."

You can use "She is gone" on its own just to say "she is no longer here." You are referring to a present state e.g. -Oh, Where's Mary? - She's gone (i.e. she already left). It's equivalent to "she is not here."