For further clarification, your official roster can have as many girls on it as you want, and it should include your varsity players, JV players and your Freshman/JV B -> ??? players. For instance...my official roster I turned in had 23 girls on it.
But for tourneys you are only allowed to have 18 players in your dugout, and they must all be in the same uniform or they can not play in the game. So if you have 40 girls on your roster only 18 can go to the game, lets say you win that game, you could have 18 new players in the dugout for game two, and so on. the 18 is how many can travel to tourney and be in dugout, not necessarily how many are on your roster.