There isn't much wrong here until you actually click on the account that she has tagged which leads to nothing more than a bot account, which has no tweets but does have 674 followers and has been on Twitter since May 2010.
Tiffany does have a Twitter account and despite her sister's mistake she did retweet it so there can't be any hard feelings there. But predictably critics of the Trump's weren't going to let Ivanka off so lightly and mockery soon followed.
Still, at least Ivanka wished Tiffany a happy birthday on Twitter. There is no sign of either Eric or Donald Trump Jr publicly wishing their sister a happy birthday (the latter of which was hanging out with UFC fighters) and Trump spent most of her birthday spreading conspiracy theories and being obsessed with Joe Biden. Still, perhaps they spoke to her privately, as not everything has to be done in the spotlight.
Thankfully Tiffany's mother, Marla Maples, didn't forget and did post a birthday message to Tiffany on Instagram.