Trying to hash together something based on the various ideas put forth. Obviously, this is only written from the perspective of Sabrina speaking; if Mami wants to make additional points, that's outside of this scope.
It's easy to say "drop the lichbomb", but there's numerous ways to present that info, and the lichbomb is composed of several individual points.
Basic progression looks like this:
1) about being a magical girl (topic intro)
2) deglamorize
3) risks?
4) soul gem/lich
5) reasoning
6) kyuubey deception
Needs to allow for secondary considerations (eg: you're still human). The info on Kyuubey being deceptive can lead into what he's being deceptive about, or it can go at the trailing end as a caveat against his misinformation. The actual soul gem statement can be at the start, or in the middle. 'Deglamorize' can present several different methods, some of which also mesh with the 'reasoning' section. The reasoning is an explanation to balance the soul gem effect with the risks of being a magical girl.
And all of it needs to walk the tightrope between the danger issues of all four girls.
Writing up varying approaches. They're not complete, but they give a general idea of the focus of the conversation.
Option 1:
This one focuses on Kyuubey as the 'villain', so moves the Kyuubey deception to the top.
[] It's about being a magical girl.
[] Kyuubey paints a rosy picture of what being a magical girl is about, but he leaves out a lot of details. And, as they say, the devil is in the details.
[] One such detail is exactly what happens to you when you become a magical girl.
[] Your soul is actually removed from your body and placed in a piece of jewelry — a Soul Gem.
[] Your body still works, but the thing that is 'you' is a separate object. Take it too far away and your body stops working.
Option 2:
This one focuses on the risks.
[] It's about being a magical girl.
[] Despite how it may look from the outside, it's not all fun and games. There are risks and difficulties that you face every day that you'd never have imagined.
[] You're constantly risking your life. While that may sound trivial and cliche, it's no laughing matter. Your body can be torn to shreds, and you'll feel every bit of it, but you'll still keep moving — as long as you still have your soul gem.
[] Because your Soul Gem — this little trinket — is now where your soul resides. If you make a wish, it's taken from your body and put into this little object.
[] Kyuubey won't tell you about this. There's lots of things about being a magical girl he won't tell you.
Option 3:
This one focuses on soul gem and consequences.
[] It's about being a magical girl.
[] This — this shiny piece of jewelry — is a Soul Gem. It means exactly what it says. This is my soul.
[] You saw it when I made a wish, right? The light that was extracted from my body and turned into this orb? Well this is where 'me' is, now.
[] There are numerous risks and dangers to being a magical girl. Kyuubey would tell you that this is necessary for you to be able to fight, but more likely he wouldn't tell you anything at all.
[] There are many things he won't tell you about being a magical girl, because there are many things that make your life — and the lives of those who care about you — far more difficult than you'd imagine. You don't realize what you're giving up until it's already happened.
Option 4:
Play up the secrets.
[] It's about being a magical girl.
[] A magical girl is all about secrets. Secrets that are kept from others, and secrets kept from you. Kyuubey is a master at playing with secrets, but there are some you need to know before you even consider thinking about making a wish.
[] One of the first is this — a Soul Gem. It's where your magic resides; but more than that, it's where you reside — your self, your soul. This is, quite literally, the soul of a magical girl. This is me.
[] Your body can be torn to shreds — and you will feel every bit of that — but you can still keep functioning as long as your Soul Gem is safe, because that's where you are now. Sort of. In a metaphorical, true self sense, I guess. I mean, your body is still you, and you're still human, but the Soul Gem is also you. Well, it's tough to deal with, and it can be tough to deal with others once you realize this.
[] And it's not like that's the only secret you have to deal with. There are many things he won't tell you about being a magical girl, and many things you may not even realize you've lost until you look around and they aren't there anymore. The people you care about, and the people who care about you... Don't think that a wish will necessarily make things better.
There are other variants. Anyone like to offer an opinion on what you think the best focus and order sequence is? What to emphasize, and what to downplay? What to bring up, and what to ignore?