Is it normal to believe in these kind of relationship?

(i'm asking for my sister) she met this new guy about a year ago while were at a girls night out thingy.. So i realize that they still talk and she is kinda seeing him yet he's far away overseas for Business. She says she's in love but i'm afraid she might be dissapointed in the end. First mistake she slept with him the night they met, they Have been calling and texting each other everyday, they sext alot.. I mean she's given herself all to this guy, do you think their relationship could work on the guy will be back next year and they already have many plans.. Im afraid for her.. Do you think it can actually work?