It appears Tiffiny is currently on holiday, based on the picture she tweeted (above). Interestingly, her twitter profile was recently updated, the words "trainer on The Biggest Loser" were removed and replaced with simply "author". In short, her bio section was changed.
On a different note, a lot of people have been wondering if Tiff is still the ambassador for Proskins Slim. While there has been no official word, she hasn't spoken of the product since early 2012 and all trace of her has been removed from their official website. Take from that what you will.