She ran away leaving her land in deep winter then was prancing about on a mountaintop singing about how wonderful and free she was without giving her people a second thought.
She didn't know she'd left the land in deep snow. She'd been repressed her entire life and was terrified of hurting people. Keeping her distance, or running away, was how she tried to protect others from her uncontrolled powers. Finally being free to be herself and use her talents without hurting anyone (as far as she knew), after years of repression, is worth a song and dance.
She struck her sister twice - ok, the first was a mistake but you'd think she'd have learned her lesson by the second time.
The second time was an accident too. She always lost control of her powers when she was frightened, and she was frightened pretty much all the time. When Anna told her she'd left Arundel in snow and Elsa didn't know how to fix it, she was absolutely terrified. She didn't know she'd struck Anna - look how horrified she was when Hans told her.
When Anna came to ask for her help she basically told her to fuck off then created a snow monster to chase her over a precipice (after striking her, as above).
She told Anna to fuck off because she honestly thought it was the only way she could protect her - by staying away. Since Anna wouldn't go, Elsa created the monster to MAKE her go. She was trying to keep Anna safe. Even when the monster caught them (Anna was stupid for throwing a snowball at it), all it did was scream "Don't come back!" at her. She cut the rope herself.
Plus who would be happy living in an ice palace alone in the mountains?
The Snow Queen!
How did she eat? What did she do all day?
She's got magical powers. I'd never get bored of using those, and she was probably powerful enough to find or create food by magic. She wouldn't need much.
The other bit that bothers me is the 'sexy' hip-swinging walk she does when she first puts on the frozen dress. It's totally unnecessary. Why, just why?
Because she was FINALLY FREE. She'd been repressed for years and finally she could express everything inside her, including her Disneyfied sexuality. She was shedding her old good-girl self; that justifies a sexy walk.
Characters need to be flawed. It's necessary to make them real and give them plots and stories to develop.
Possibly overthinking this.
Me too.