Should I tell her?

My sister has been getting in her fair share of trouble since I left for school last year.
To be honest, she got in some before I left, but its only gotten worse since then.

As of right now, she's grounded for a very long time. And if she screws up this progress period, my mom wants to take her out of school and put her on home studies. The only problem with this is that no one would be here to watch her, since mom works.
To solve this problem, mom wanted to put in a security system so she would know if my sister tried to leave during the day. The only problem with this is, we're super stressed out over money right now because of school. (Though a lot of our concerns were put to rest this morning, that's for sure.)

Anyways, all of this is coming to a head now because when she gave me her phone after getting home from school (she isn't allowed to have it for anything other than calling mom, which she can do from the house phone), she got a message. So Robbie and I knew she had been texting. While looking to see how many messages had been sent, and at what times, we ran across some messages that definitely should not have been there. And not about ditching or smoking cigarettes or anything, dirty messages that should NOT have been there.

So now I'm faced with a dilemma. I could tell my mom, which would stress her out beyond all belief, and then me leave for school this week. Or, I could ignore that this is happening, my sister will wind up being pregnant, and her life will be fucked. Or, I can go in and see her guidance counselor Thursday (he was also mine, and boy did we have our fair share of meetings). I'm going with door three. It's his job, right? He should know what to do with minimal stress on everyone involved, right?

For now, Gabbie is afraid that I'm going to tell mom. Hell, I'm afraid that I'm going to tell mom. What if it just slips out? If I'm angry and everyone starts yelling and it just comes out?

Our entire homelife would fall apart, that's what would happen.

But she is afraid of me right now. She didn't even argue when I told her she had to do the dishes. It was actually my turn, but at the same time, Robbie and I cleaned the rest of the house. Only fair if you ask me.