Please clarify: Is this a private, religiously affiliated school? A Catholic school or conservative Protestant school? I ask because I can't see a public school allowing this group to meet there as a school-sponsored activity during the school day. I feel sure the group must be the Fellowship of Christian Athletes -- does that sound right?
If this is a public school, well, they are out of line, and this would require some investigation to see why this happened in the school day. This group does meet outside school hours in some schools, I think, but during the school day seems strange. I would question whether the school (again, if it's public school) knows the content that's being presented and whether it's age-appropriate. If the school says "We're within the law to allow this group during school hours," and you have an issue with it, tell your child not to attend again.
If this is private religious school, parents know that whatever the school's basic beliefs are will end up being presented to the kids in many forms. Enrolling your child there means you give implicit consent to their religious and social teachings being presented to your child.
If this is private religiously based school, I'm not as sure what the problem is unless you feel your child was too young to hear about abortion yet, or the presentation used graphic images or language, or -- this would be the big sticking point -- you object to the idea that abortion is never an option. If you object to that, and the school teaches something you don't believe, reconsider whether your child should be schooled elsewhere. Even if your child is exempted from these specific Fellowship of Christian Athletes meetings, she will encounter this again repeatedly over the years there. That's fine if you have her in this school to get this specific faith's perspectives and you share them.
You could attend the next one of these meetings yourself. You could also talk to whoever is the faculty adviser for the group and ask to be informed about what was covered. Is the issue, for you, that the topic came up at all for kids her age, or that it was presented in some graphic way? Not clear from the post.
I don't know what the Life Line is but it sounds as if it might be a protest, or an activity handing out information, or possibly a presence outside an abortion clinic--? It seems to be related to interacting with women who are considering abortions. Find out the specifics from the school or the organization, rather than your child, because if you child wants to go, you really need to decide if you are OK with it or not. I would at this point be more concerned with the fact "they invited everyone to participate in the Life Line they were doing in a couple of days." If you, and she, are behind it, then let her do whatever it is, and even go with her. But you do need to know what it is, and ensure that there was not pressure put on kids to attend or do something that may be a problem for you, or too much too soon for her.