Emily Bowen, 18, was jailed for 21 months in August after being convicted of injuring Molly Young, then 17, with fluid containing sulphuric acid.
Bowen poured drain cleaner into her viola case after Molly had started dating her ex-boyfriend.
She suffered wounds when the liquid spilled from the case and on to her legs.
The Scottish Prison Service has written to Molly to tell the teenager that Bowen was being released.
It is understood she has been given a home detention curfew imposing restrictions on her movements and that she will be living at her parents’ home in Haddington, East Lothian.
A source close to Molly’s family said: “She is still affected by what happened and hasn’t received any sort of apology from Bowen.
“The letter informing her of the release didn’t come as a surprise. The family had been warned Bowen would be released earlier than they would like.
“There’s been a rise in acid attacks and the soft sentence was difficult to accept.
“Bowen’s early release is hard to comprehend but there’s nothing anyone can do about it.”