"When you see something like that, your heart starts beating, you break out into a little sweat, like, 'What on earth just happened?'" she told The Washington Post.
"We had Christmas lights outside, but we don't have the '[National Lampoon's] Christmas Vacation' lights," Horomanski said.
"And I'm looking at my Christmas tree, and I'm like, no, that wouldn't have caused it."
There was some good news though — if you could call it that — as Horomanski's statement said that she didn't have to pay the entire amount until November 2018. Rather, her minimum payment for December was $28,156 ($AU36,469).
"It wasn't due until November of 2018. It was like, well, I guess we have a year to come up with this billion-dollar bill," she said.
Once she had recovered from the initial shock, Horomanski contacted her son who got in touch with Penelec who, thankfully, reassured him that it was an error.
Horomanski's actual bill was $284.46 ($AU367), with Mark Durbin, a spokesman for Penelec, saying he wasn't sure what had caused the error.
"I can't recall ever seeing a bill for billions of dollars," GoErie reported Durbin as saying. "We appreciate the customer's willingness to reach out to us about the mistake."
According to Horomanski the whole ordeal gave her an idea about what she wanted her son to get her for Christmas.
"I told him I want a heart monitor," she said.