The author's new novel, Better Together, has shot to number one in original fiction in Ireland.
She said she was nervous about her book being released when 50 Shades was taking the world by storm.
"I'm always nervous when the book goes out; I've had so many books out and you still never know, particularly with 50 Shades of Grey. It shows that people are going for erotic fiction, but fortunately they didn't stop buying mine.
"I've read small parts of all of the trilogy. To be honest, I love characters and I think the woman in 50 Shades is so pathetic that I couldn't get past her.
"She's meant to be an intelligent woman, but she's just too silly for words."
The author said the book failed to keep her attention.
"People can read what they read and I wouldn't judge them for what they read, but for me it's too boring. Even the sex didn't keep me going.
"I think it's just that, at different times, different things become popular and capture people's imagination. Word of mouth helps; people start saying, 'You have to read this', and then people feel they're obliged to read it in case they're missing out on something.
"I did [feel obliged] but it's not something I would have felt any great desire to read. When people were telling me to read it and I was being asked about it, I felt I had to."
Sheila's new book focuses on the current economic crisis and job losses.
"The girl loses her job, so the current environment was on my mind, and people who are having to do things they wouldn't normally do because of a change in their circumstances.
"She has to move out of Dublin and move to a small town. The newspaper industry is going through a lot of changes, so I was thinking about that, and I felt that what happens to my character is something that can quite easily happen."
Sheila is currently in Seville in Spain researching her next novel, which she expects will take around nine months to write.
"Before I write, I spend a couple of months thinking about the character and then I spend six to seven months writing it, and then I'll do two months editing.
"All I hope is that the people who buy it, enjoy it. People are spending their hard-earned cash on my book, so they should enjoy it.
"My biggest dread is when I get to the end, and think why did I finish that?"