AITA if I tell my stepsister to stop being so entitled?

The usual, first post/ on mobile blah blah blah... sorry gonna be long.Little backstory. My (22F) mother met my stepdad 8years ago, I’m my mother’s only child, where as my stepdad had 3 children already (the other kids aren’t a part of this so I’ll leave them out of it). SS was 10 when we met she is now 18. The mums great, got on well with us all after and stepdad would help her out with money stuff when she was out of work.To this year, she is now in uni, after getting top grades A+ across the boards. I’ve seen how great my Stepdad treats SS, helping her study, getting her a laptop to help study (MacBook Air, so not just some tat, he wanted it to last her). He’d even tell her she’s studies too hard and he worries about her. He’s always been supportive of everything she’s done (too al his kids tbh)And then today, I see on her second Instagram account that she’s posted about “having an unsupportive family” and “Thankyou dad I’ll save money for New York just to spite you. “ even the mum responded to it with a joke?I know that SS and SD had a conversation recently about just how things were going and he did mention to her maybe it isn’t great to spend stupid amount to go to New York when you are at university. Not sure how it ended but it definitely wasn’t an argument.I haven’t told my stepdad this cause I don’t want to upset him considering he’d literally walk through fire for his children and she slates him online where he can even see cause it’s private.So WIBTA if I told her I saw it and that it’s actually just really disrespectful.TDLR. Stepsister has parents who would die for her but for some reason saying saving money for a New York isn’t the greatest idea makes them unsupportive. https://www.reddit.com/r/AmItheAsshole/comments/eiq4h2/aita_if_i_tell_my_stepsister_to_stop_being_so/?utm_source=ifttt