The Emmerdale actress, who recently teased her return to the soap as Scarlett, told the Daily Star that rumours about her being pregnant were "horrible to read", but made her realise she wanted to address her size.
She explained: "There were lots of nasty comments and stories all over the internet. There was this massive rumour going round that I was pregnant.
"There was one particular comment that said 'Is Kelsey-Beth Crossley pregnant?' and a reply that said, 'No, she's just really fat'.
"At the time it was so upsetting and it was horrible to read. But it did make me sit up and listen. I thought, 'I really needed to sort this out'.
Despite the negative experience, Crossley said that she understands it is the nature of appearing on television.
"That's what the industry is about. As soon as you appear on telly, people pick you to bits," she said.
"I'm happy with my weight loss and I know I'm not stick-thin.
"I've just been working out in the gym and feel sexier than ever. Everything feels really toned.
"I've lost the weight safely with Slimming World which means no food is banned. I still have the odd cheeky McDonald's."
Crossley added: "Emmerdale has so many sexy ladies and it's nice to be part of a cast of strong females. I'm excited for people to see me on telly and see what I look like now.
"I hope I don't look at myself and still think I need to lose more, because I'm really happy in real life when I look in the mirror and that's the main thing."
Crossley returned to screens on Wednesday, October 31 in the aftermath of Carl King's death.
> 'Emmerdale' funeral, Corrie ultimatum, 'EastEnders' kiss, 'Oaks rage
> Spoilers: Nicola and Scarlett vow to fight Charity
> 'Emmerdale at 40' documentary grows to 3.6 million