The 19-year-old, who describes herself as Wales's answer to Beyoncé and names Katie Price as a role model, announced on the social networking site that she had been urged to commit suicide following the MTV show's premiere last night (September 25).
"I don't mind the abuse but telling me to go kill myself is sick #b**tards," she wrote.
When she started retweeting a few of the messages in question, Hagan warned her: "if you retweet bad things you will get more because people just wana RT or argument, don't give em satisfaction trust me."
Glamour model and ex-Celebrity Big Brother contestant McLean added: "That's so true babe I can't help myself sometimes but it's not worth it...just do your thing babe xxx loved the show."
Hagan continued: "I know better than anyone [about abuse], couldn't leave my house after series 1," to which Grace replied: "That's how I feel."
Grace has already stripped off for a Nuts photo shoot with Valleys co-star Natalee Harris.
The show has quickly been condemned by Welsh MPs and politicians, who branded it "dull, cheap, tacky and over-promoted".
The Valleys continues Tuesdays at 10pm on MTV.
Watch Digital Spy chat to the boys and girls of The Valleys below: