This was one of our favorite ABC After School Specials growing up. Like the other comment says, a family inherits an island that is not claimed by either the US or Canada -- and when they put a clothing item up on a flag pole so someone can find the island they are on, this is mistaken for a symbol that they are starting their own country.
I can't remember much else, but I do remember that Sarah Jessica Parker's character idolizes Princess Di; and that she learns being a princess is not as much fun as it appears to be from reading magazines. If I remember correctly, though, a hot prince comes to hang with her and she is smitten.
I'm not sure what the moral of the story was supposed to be -- most of the ABC After School Specials carried messages -- but maybe it was to show that being famous and important is not all it looks like it may be. Whatever the case, when my brothers and sisters and I saw this on, we cheered and were glued to the television set.