A Long Island woman has been arrested for allegedly harassing an upstate tot who suffers from a rare genetic condition that causes her skin to crack when exposed to air, police say.

Krista Sewell

“I have no idea why she chose to do this,” the 2-year-old child’s mom, Jennie Riley, told The Post on Sunday, referring to 26-year-old suspect Krista Sewell of Melville.

“This last year has had many difficult moments, but we have great relief in knowing that she has been arrested,” the mom said of Sewell.

Riley’s daughter, Anna, was born with a condition known as “harlequin ichthyosis,” which causes her skin to thicken and crack as soon as it is exposed to air. The painful cracking creates open wounds all over the body that can resemble those of harlequin characters’ diamond-shaped costume patterns.

The tot’s daily care routine includes three hours a day in a special moisturizing bath, another hour getting her hair combed to prevent her follicles from getting clogged and more time having lotion applied all over her body, her mother told The Post in October.

Riley chronicles her child’s life on a Facebook page titled “Hope for Anna.”

But the Ulster County mom wrote on Facebook on Friday that she and her daughter, as well as another ichthyosis sufferer, had been targeted by a hater.

“Countless messages, emails, and comments have been sent to us all much to graphic to share. It is not only not ok to send these types of messages it’s also illegal,” Riley wrote.

State police busted Sewell on Thursday for allegedly threatening the young child on Facebook, Instagram and GoFundMe and in letters mailed to her family’s home.

Sewell was charged with felony aggravated harassment as a hate crime and is being held at the Ulster County jail in lieu of $25,000 cash bail or $50,000 bond. She did not immediately respond to a request for comment through the jail, and a relative hung up on The Post when reached by phone Sunday.