When the teenager responded to ask why she had been turned down, Shantel replied: "Just not engaging. And answers we're 'like' basic."
Basic is a term, originating in the US, which describes cliched or unoriginal behaviour.
Shantel then used the emoji which depicts someone laughing so hard that they're crying.
Speaking today to MailOnline, Megan, said she 'couldn't believe' how unprofessional the steakhouse chain were.
Describing the interview with Shantel, she said: "I thought it was strange she didn't shake my hand, I thought she would have been more professional.
"She had her phone out for the entire time, I didn't really feel like I was in an interview."
Megan asked when she would expect to hear back about the position, to which Shantel said she would be in touch in a few days. She then received the text.
She said: "I can maybe understand why my answers were basic, but I haven't really had many interviews before.
"Shantel was asking about my proudest moment but I'm only 18 so it's not like I can say my kid or my marriage. To text me a minute after I'd walked out saying that is nasty."
She said she was so shocked and now wish she had returned to confront the interviewer.
"I was so shocked and I wish I'd gone back in there," she said. "My mum was so angry - these big companies can't treat people like that. It has definitely put me off the company.
"For people who might not have any self confidence as well, it could really upset them."
Megan also claimed the assistant manager had behaved poorly during the interview, by not having a copy of the teen's CV to hand and drinking coffee throughout.
A spokesman for Miller and Carter told the paper: "We can't apologise enough to Megan.
"It was never our intention to be disrespectful or upset her in any way. The texts were sent in error and were intended for our manager, not the candidate."
The company has vowed to investigate.