Do you think she may have been molested?

My husband and I are extremely concerned because we have seen a decline in her attitude in the past few months as far as being completely anti social and having no outside interests.  Has anyone experienced a similar situation? I am meeting with my pastor today to discuss this.

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So, I don't mean to armchair psychoanalyze, BUT: kids have always acted this way as they started to develop into adolescence.  What used to happen, when they started to ask questions about themselves and the world around them, is that they'd go smoke weed, listen to heavy metal, maybe jump off a roof into a swimming pool, commit or entertain impurities, and read Ayn Rand.  Dangerous, often sinful stuff.  But not exactly a rebellion against the natural order.
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But now there's a whole new brand of nastiness available, and it's the gender-fluidity/sɛҳuąƖ identification garbage.  TWenty years ago your daughter wouldn't even remotely CONSIDER that she's anything but sɛҳuąƖly normal.  But now everybody has some deep, soul-searching, ontologically radical epiphany about "what they really are" vis a vis "sex and gender" and because of that, instead of you finding weed in her sock drawer or her telling you that John Galt is her hero, she's dropping these types of bombshells.
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In other words I agree, it's a "phase," but not one to be taken lightly.  It's predicated on her finding credible some very bad ideas about the natural order.  Just telling her that God doesn't want her to be a pansɛҳuąƖ is very probably not going to "work."  If she thinks she is a pansɛҳuąƖ then she either thinks that God DOES want her to be, or that what God wants doesn't matter.  You might have to go into greater detail.  You might have to commit to explaining things in ways you'd prefer not to.  Like, "sodomy is wrong" sort of stuff.  Because that's what this is all about.  She's bought into this "sɛҳuąƖ identification" stuff which is all (allegedly) about personal freedoms, individuality, "being who you are," etc.  Well, some people are angry and that doesn't mean to "be themselves" they have to murder.  Some people are lustful that doesn't mean that to "be themselves" they have to go raping.  Some people are greedy, that doesn't mean they should steal.  Are some people attracted to the same sex?  No idea, but even supposing they really are, doesn't mean they should go off sodomizing.  You'll probably have to make it about that.  Otherwise she'll just think it's an attack on herself, which'll probably just make her commit even more to the pansɛҳuąƖity and probably seek allies who'll only further reinforce it.
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Other poster who asked if she was molested is right to ask that, too.  I think there's enough intellectual rot nowadays that kids can get stupid ideas about sɛҳuąƖity and even commit to those ideas without external influence of molestation, but there's definitely a high rate of correlation between being abused and being attracted to debauchery.

Sounds like she goes to public school, maybe a Novus Ordo mass once in a awhile, or Protestant service, watches television, Facebook...….. in other words she is living a worldly life, never having lived the faith. One can only lead by example, and it looks like the example she has been given is that religion is just being nice to people.

Now she will be a nice lesbian caring for people, and go to hell when she dies.

Sounds like she goes to public school, maybe a Novus Ordo mass once in a awhile, or Protestant service, watches television, Facebook...….. in other words she is living a worldly life, never having lived the faith. One can only lead by example, and it looks like the example she has been given is that religion is just being nice to people.

We go to Mass every Sunday.  She does go to public school but attends Religious Ed classes.  She isn't on social media but does have internet access.  This was probably my mistake for allowing it and not monitoring it close enough.  I think there are a couple kids at school who feel the same way.  I promise you that she has been taught way more that the idea that religion Is "just being nice."  She has a 14 yr old brother who is nothing like this and is being raised the same way.

I will ask her about sɛҳuąƖ abuse but I am just about positive that's not the case.  There would be no one in our family that I would suspect, but I know if could be someone else.  And before you ask, I am positive her brother hasn't molested her.

I don't deny her feelings but at the same time I've told her that leading her life as a pansɛҳuąƖ is not God's plan for her.

I'm not sure what you mean by "deny"-ing the feelings.  It almost sounds like you're validating them as somehow legitimate.

She does go to public school 

That would explain it. 

Sending children to public schools nowadays is simply not an option for Catholic parents, or any sane person, really.

Homeschool your children no matter what sacrifice you must do. Your daughter's soul will be corrupted if you don't. Pull her out of those Cultural Marxist indoctrination machines.

- Cantarella

OP,
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Do everything you can to get your girl out of that school.  She's not just being exposed to those ideas, but that environment is responsible for encouraging, enabling, and empowering her "pansɛҳuąƖism." 
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If you think you can't homeschool, remind yourself that this is now your life: public school has eight hours a day to ruin her, five days a week.  You have, what, four hours a day to undo the ruining?  Do the math.  Even with the weekends, at very best you're just going to be able to "reset" her to "zero."  And you're going to require her to live a double life in order to do that.  You don't think she'll notice the hypocrisy of sending her to the indoctrination studio five days a week while you spend the rest of her waking hours trying to "undo" their work? 
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Not only will homsechooling be more efficacious in achieving the end result, I suspect it will be less exhausting than the alternative.