I get how you can "show" for example the story of a woman who is sad by merely describing the stars in the sky, but how do you describe the intensity of her emotion in a poem? I think you can do it by describing the sounds and movements, but in certain situations, like when you describe the stars in the sky, you can't really express the intensity of an emotion by doing that (stars don't make sounds, star can move quickly, but shooting stars are not associated with sadness). Aside describing movements and the sounds of a scenery, is there anything else I can do to express the intensity of an emotion by showing and not telling?
Emotions drive actions. You show the actions, or the lack of actions, that result.
A profoundly depressed person will not even wash themselves, they have no motivation to clean their residence. They will miss appointments. They may not even feed themselves, or will feed only on stimulants like chocolate.
Sad people cannot find humor in anything, and in fact may find humor an irritation.
Sad people cry. Sad people may be fatalistic, without hope. They can withdraw into themselves and become so self-centered they care about nobody and nothing, and everything they see is in a dark light. We'll all be dead soon. Our lives are a waste. Nothing we accomplish will last, or be remembered.
Even their dreams may be nightmares.
Emotions of all kinds drive actions, and attitudes, and outlook on life.
Show Don't Tell means don't tell people she is sad, show her living her life in a way that lets the reader realize for themselves that something is wrong, and then that the something is sadness.
Like the song; "Alone Again, Naturally":
In a little while from now,
If I'm not feeling any less sour,
I promise myself to treat myself
and visit a nearby tower.
And climbing to the top,
Will throw myself off,
He says he is "sour", but that could be anger, it isn't "suicidal". Visiting a nearby tower might cheer him up, it sounds like a plan, until the next line.
His words and thoughts betray the depth of his grief and sadness; in his mind, suicide would be a "treat".
The descriptors work equally well in prose and in poetry, only the meter really differentiates them objectively. Though modern literature is sparse with deep prose, it is still relevant. Consider first, David Copperfield:
The gloomy taint that was in the Murdstone blood, darkened the Murdstone religion, which was austere and wrathful. I have thought, since, that its assuming that character was a necessary consequence of Mr. Murdstone’s firmness, which wouldn’t allow him to let anybody off from the utmost weight of the severest penalties he could find any excuse for. Be this as it may, I well remember the tremendous visages with which we used to go to church, and the changed air of the place. Again, the dreaded Sunday comes round, and I file into the old pew first, like a guarded captive brought to a condemned service. Again, Miss Murdstone, in a black velvet gown, that looks as if it had been made out of a pall, follows close upon me; then my mother; then her husband.
It would be very hard to have any conversation about sadness and poetry, without including Edgar Allen Poe. Here is The Conversation of Eiros and Charmion
EIROS. Oh God!—pity me, Charmion!—I am overburthened with the majesty of all things—of the unknown now known—of the speculative Future merged in the august and certain Present.
CHARMION. Grapple not now with such thoughts. To-morrow we will speak of this. Your mind wavers, and its agitation will find relief in the exercise of simple memories. Look not around, nor forward—but back. I am burning with anxiety to hear the details of that stupendous event which threw you among us. Tell me of it. Let us converse of familiar things, in the old familiar language of the world which has so fearfully perished.
EIROS. Most fearfully, fearfully!—this is indeed no dream.
CHARMION. Dreams are no more. Was I much mourned, my Eiros?
EIROS. Mourned, Charmion?—oh deeply. To that last hour of all, there hung a cloud of intense gloom and devout sorrow over your household.
CHARMION. And that last hour—speak of it. Remember that, beyond the naked fact of the catastrophe itself, I know nothing. When, coming out from among mankind, I passed into Night through the Grave—at that period, if I remember aright, the calamity which overwhelmed you was utterly unanticipated. But, indeed, I knew little of the speculative philosophy of the day.
Why need I paint, Charmion, the now disenchained frenzy of mankind? That tenuity in the comet which had previously inspired us with hope, was now the source of the bitterness of despair. In its impalpable gaseous character we clearly perceived the consummation of Fate. Meantime a day again passed—bearing away with it the last shadow of Hope. We gasped in the rapid modification of the air. The red blood bounded tumultuously through its strict channels. A furious delirium possessed all men; and, with arms rigidly outstretched towards the threatening heavens, they trembled and shrieked aloud. But the nucleus of the destroyer was now upon us; even here in Aidenn, I shudder while I speak. Let me be brief—brief as the ruin that overwhelmed. For a moment there was a wild lurid light alone, visiting and penetrating all things. Then—let us bow down, Charmion, before the excessive majesty of the great God!—then, there came a shouting and pervading sound, as if from the mouth itself of HIM; while the whole incumbent mass of ether in which we existed, burst at once into a species of intense flame, for whose surpassing brilliancy and all-fervid heat even the angels in the high Heaven of pure knowledge have no name. Thus ended all.
These are spectacular visuals using light and sound and even heat to paint the sadness and despair. In poetry, a star can certainly make a sound.