Okay, everyone seems to be really confused with what's going on in the story right now. For those of you that don't get it, please read these quick notes! If you do get it, you can skip over this! Thanks! Keep reviewing! Yeah! By the way, some of the things I may mention here will never actually be known to the characters in my story, but the Elders will know it, so I can still write it! – Let's just say that you'll know more than Piper, Prue, Phoebe, Paige, Leo, Wyatt, and Chris, okay? Good!
The only way for Phoebe and Piper to meet Prue again was to accept the fact that she was gone forever. Reasoning: when Prue first died, Grams had told Piper and Phoebe that they couldn't summon her because they hadn't yet accepted the facts.
When Paige realized this, she made Phoebe and Piper state aloud that Prue was dead, so that she (Paige) could finally meet Prue. However, what Paige didn't realize was that there are loopholes to this plan – emotions. You see, though Phoebe and Piper said aloud that their sister was dead, they still couldn't really accept that in their hearts.
Because of this loophole, Prue was only, shall we say, half-there; she could only be whole-there if everyone truly understood that she wasn't going to come back, and that they had to leave her in the afterlife (unless there was an emergency and they had to summon her, of course).
When Piper accidentally ran into the circle of candles, the Elders decided to punish the Halliwells (and Leo). Yes, I know, it wasn't very nice of them, but the Elders don't like it when people fool them, so they didn't really care! So, they decided that that would be the perfect opportunity to punish: make Piper into a passed spirit.
However, the Elders then realized that if two of the four Charmed Ones couldn't use magic properly (and were also scared out of their wits of what might happen to Piper), then the world was basically in trouble – especially Wyatt and Chris, who are the next generation of magic anyway.
And now, let our story continue to unfold!
PS – YES, I WILL CONTINUE THE STORY AFTER THE CURRENT PROBLEM IS SOLVED – NEVER FEAR, YOUR AUTHOR IS HERE! (da da da da da da...)