It depends really. If she's just having her "fun as a youngster" now and is OK with it ending / transitioning into a more adult life later then, as with anyone, it could go either way
. She is only in her early 20's and a LOT of people that age (unfortunately) still act like kids / teenagers. It doesn't
necessarily mean she'll never grow up.
On the other hand... if she thinks that the way things are for her now will last forever, that it's her whole life rather than an experience that will most likely come to an end completely within the next few years, then yes she's in for a disappointment.