The Woman Who Saved the World by Susan Palwick, published in the May 1985 Asimovs and available on Internet Archive
A woman is grocery shopping (or just finished) and in a bad mood — people are rude, her kids poorly behaved and U.S.-U.S.S.R. tensions very high.
Actually, she's just walked away from her house in disgust - her husband is a gambling addict and her son is a delinquent. No mention of war at this point.
She is questioned by an alien in human form who asks her about the world and in irritation, she lies — everyone is kind, kids are great, etc.
She's questioned by the alien in barely human disguise at a bus stop, and lies deliberately hoping that the alien will abduct her husband and son (and maybe her neighbors, too).
The alien says (something like), "Oh, no. Our research has degraded your planet — we'll fix it."
“Thank you,” came the soft voice in her head. “That was most useful. And these are common characteristics of your species?”
“Oh yes,” Jeannine answered, hoping it wouldn’t hear the quiver in her voice. (How could it understand her, anyway? Translating machine? ESP? However it managed, it seemed to be having no problems.) Struck by inspiration, she gave it a brief report on her charming neighbors — who were in fact filthy and hostile — and those wonderful girls on the Acme checkout lines, who in reality overcharged Jeannine whenever she went into the store. Maybe the alien would kidnap all of them. It was at least as likely as her having been chosen to give the report in the first place.
The raincoat rustled, and the voice sighed, "Very informative ... if you’ll allow me to monitor — ah. Yes, I was afraid of that. Sometimes visitors have unpleasant effects on the local habitat, upsetting delicate balances, creating disorder . . . my instruments reveal that such has indeed been the case here.”
Next morning, the kids are behaving, peace has broken out, and at the grocery store when she's a dollar short, the person behind her in line gives her money.
It's actually later that day:
The husband:
“Jeannine, dammit, let me finish! Jen, look, I was going to the track. I was. Joe Megan was giving me a lift, and all of a sudden something happened and I said, 'Joe, take me home, I must be sick. . . .’ Like a little kid going to the circus who gets scared of the elephants, Jen . . . we’d just started out; it couldn’t have been more than twenty minutes ago. And you know what an SOB Joe is, and he was in a rotten mood ’cause we’d gotten going late. I thought he’d gripe about coming back, but he just smiled and swung the car around. Like he didn’t mind at all. Don’t you see — ” "All I see is that you’re here goofing off while the car’s sitting stinking in the driveway, and we can’t fix it!”
He relented, sighing, and said, "All right. All right, Jen. It’ll be fixed soon. Because I don’t want to gamble anymore. Only — Jen, I don’t know what changed. And I don’t know what to do instead.”
The son:
“Mr. Andersen was showing me how to work his lawnmower. He’s doing it this time, ’cause the grass is so shaggy, but I will from now on.” He blinked at her and said, "They’re going to give me five dollars a week. That’s pretty good, isn’t it? For a little lawn?”
Peace:
On an impulse, she flipped open the newspaper, to find the front page filled with the headlines "Ceasefire in El Salvador,” "Peace Talks Resumed in the Middle East,” and "Lull in Gulf War.”
Grocery Store:
“I don’t understand,” Jeannine protested, unable to bear this weight of observation. “I had more money this morning, I know I did. It must have fallen out of my bag somehow.”
“Here,” came a woman’s voice from the line behind her. Jeannine turned, panicking, to find someone holding out a quarter. “Here, take it — we all get caught a little short sometimes. It’s all right.”
The alien reappears to say that he's restored the world to the way she reported it should be - and she realizes that she's unchanged as an unhappy, not-very-nice person in a world far better than she can be comfortable in.
The alien doesn’t come back, but
She stood there, miserable, holding the joint, and knew that by rights she should be overjoyed. She had everything she’d wanted now, the problems gone or going; she should have been happy. Anyone would know that. . . .
. . . Except the alien. The alien wouldn’t have known it, any more than it had known a lie. I didn’t say anything about myself, Jeannine remembered in pain, nothing — it was all about Daniel and Phillip, and the Andersens, and Andrea, and everybody else — nothing about Jeannine, because anyone would know that if all that were different, I would be too. Except the creature. It never looked at me, to see if I were disturbed and needed fixing. I never said anything about myself it could have changed me into.
That lovely lie, she saw now, was the same tale she’d told everyone she knew, the web she’d spent fourteen years spinning. How are you, Jeannine? (Fine, fine.) How are Daniel and Phillip? (Just wonderful.) Are you happy? (Oh, yes, of course.) The creature from space couldn’t have helped her even if it had wanted to, any more than her fellow humans had ever been able to. She’d never given them the chance.
