SOLVED. childrens/teens sister has severe disease and needs machine to breathe [s]

[Caroline]

I read this book maybe five years ago, and it was already a few years old by then. It was set sometime in the 1920s-1980s. I remember that there were two girls, the main character and her older sister who got some illness (polio?) and had to stay in a machine all of the time that breathed for her. I think they called it "an iron lung." There was a doctor who tried to unplug the machine for a few seconds to see if she would be able to breathe for herself.
The main character had a horse that she loved but eventually agreed to sell for money for her sister's treatment. I think that the horse could jump off a cliff into a lake or something.
Their aunt was staying with them, and the sick sister begged her to unplug her machine and let her die. The aunt eventually complied, and made it look like she died in her sleep.

[bookel]

Any of these or these?

It could be the below, though the one who gets polio is a boy.

Hero of Lesser Causes by Julie Johnston

[Andria]

To Race a Dream is set in early 1900s, the MC works on a horse farm and her sister has polio.

[Andria]

But this one If Wishes Were Horses specifically mentions the sister in an iron lung, so I *think* this might be it.

[bookel]

Reviews here of If Wishes Were Horses by Natalie Kinsey-Warnock.

In part:

From School Library Journal
... set in rural Vermont in 1932, Lily, 12, ... She has always felt that her parents favor her sister Emily. Lily has always wanted a horse; her sister wants a cat-and gets it. ... When Emily contracts polio, she is placed in an iron lung but her condition worsens. Lily is then torn between resentment-Emily now gets more attention than ever-and fear and compassion for her sister. After seeing a diving-horse team at the circus, Lily practices in secret with a horse that she and Aunt Nell have rescued from abuse, ... her pain at the loss of her sister.
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Fits to a T, mentions everything from the initial post. Well done!

[Caroline]

It's If Wishes Were Horses! Thanks so much Andria and bookel! I've been looking for this book forever, it was one of my favorites!