The singer exchanged messages with the rival BBC show via Twitter last week.
The Voice UK thanked Sinitta for watching the launch show on Saturday via their official Twitter account, saying: "Thanks for watching #TheVoiceUK, @sinittaofficial. Danny says hi (he's so macho)."
Speaking to Digital Spy, Sinitta said: "[Simon's] not amused. Not amused. But the way he keeps raving about Jessie J, I suspect he's doing the same thing."
The 'Toy Boy' singer went on to say that she felt Jessie J should replace the current X Factor USA judges.
"I love Jessie J and Danny [O'Donoghue] and of course Tom Jones, but Jessie J is just adorable. If I was Simon I would replace both [X Factor US judges] with Jessie J."
The singer also commented on the recent incident during which an intruder broke into Cowell's West London home.
"He's fine. He's letting things calm down. Keeping a low profile. A bit shaken up, but he's fine," she said
The X Factor judge's London home was broken into by an armed woman on Saturday, March 24.
> Sinitta on Simon Cowell house intruder: 'He thought it was me'