The rapper claimed the British singer had copied some of her ideas and that his video for Like I Would looked like the one she made for her track Yung Rapunxel.
Her Twitter account was suspended following the abusive posts.
And although she apologised shortly after the incident, she's now issued a more detailed explanation on Instagram.
"There are no words that can fully express how sorry I am," she wrote.
"Recent events have taught me the importance of taking accountability for one's actions. I want and need to say I am sorry, I was wrong.