The 16-year old took to her account on the social-networking site after seeing snaps of Styles and Taylor on a 'romantic stroll' in New York - where she accused the We Are Never Ever Getting Back Together singer of "wh*ring around."
Mathers wrote: "If @taylorswift13 is really dating the love of my life @Harry_Styles i will not be happy.!"
"Dear @taylorswift13, please stop wh*ring around with every guy you see. We all know you're only doing it so you can make another album.
"I am never, ever, everrrrr, listening to your music againnnn @taylorswift13. LIKE EVER."
After receiving some criticism for her comments, Hailie was at first reluctant to apologise, tweeting: "Getting so much hate ... But really couldn't care less xD."
However, Em's daughter later took back her remarks, stating she never realised her tweets would receive such a negative response.
She said: "Wow. I didnt mean for people to react to my tweet in the way that they have it was just a bit of fun! Sorry @taylorswift13 for my immaturity."
Mathers added: "I believe I'm entitled to my own opinion, but that got out of control. I don't understand why there are 'news' articles written about it !"
Swift and Harry - who have been branded Haylor by fans - were recently spotted holding hands at an after party for 1D's epic Madison Square Garden gig on Monday (3rd December).