@incognitoind, if the OP had described a situation where the initial thrower did a basketball pass or a one-handed toss to her teammate and the referee had called an illegal throw, I'd be right with you in suggesting a different approach to refereeing. But as described in this case, the player executed a perfectly legal throw. Nothing in the description indicated that anyone else on the field thought the thrower's intent was to have the teammate take the "real" throw. An added benefit is that the players likely learned how not to hand over the ball to a teammate. Of course I can envision a situation where the thrower popped the ball over her head in a marginally legal throw that looked much more like an attempt to give the ball to her teammate. Taking skill and experience into account, that might make a non-call more appropriate. The OP didn't see it that way, which is OK by me.
The throw-in that isn't might work for me, maybe once, early in the season, with a loud inservice, at U-littles, but no way in a HS game.
I can see the TI both ways and I would really need more information before calling handling. What type of JV girls game. Around here JV girls can range from u14 Rec to a solid class 3 (silver) team. The closer to Rec the less likely to call it. Who normally was taking the previous throwin. If it was the girl who handled probably not going to call it. If the situation called for a long throw and you got the feeling that the handler was the long thrower not calling it. Now if the handler has a defender closing on her I will probably call the handling. Again it really depends on the tone of the game and if the OP thought it was handling it is the correct call. I can see incognito's POV and we have all referreed with those refs who make the game about them but I don't get that impression from the OP. IMHO most referees who spend time on theses types of forums are trying not to be that ref.
I would also make a case coming down to the spirit of the game. Which was brought up at national camp by esse bahmarst. I honestly, think a simple delay the whistle see what happens. But I agree with icognito here. No way am I blowing the whistle. No one wants to do throw-in practice in a game.
In incognito's defense. I believe a simple delay of the whistle could help tons here. From the OP I read it as the player throws the balls, the other girl calls for it, and then catches it. I envision an immediate whistle. Whereas a simple 2-second delay and you can figure out what's going on. Especially, on a JV game. Just give a little delay and let the players figure it out. If I had players are under the impression she's conning the game and gaining an unfair advantage you are perfectly within your right to call the DFK. But does the game really need this whistle? Sounds like a yhtbt to get it.