I can see why you are concerned. It must be very frustrating to see these messages. But she can't control what other people say. If you want her to not interact with them then say that. It is okay to feel disrespected because these conversations are going on. But if she is not responding to them they are responsible for these messages. You should know if her behavior goes beyond reading these messages. If she isn't participating then she isn't doing anything wrong. You can talk about ways together that don't encourage such comments. If she cares about you she will want to stop this from happening. I think you should talk about it together beyond what you have. If you feel disrespected let her know and see what can change.
As far as her response to your friends you don't know if that was meant sexually. He could have been saying I love the girls meaning he has a lot of hookups but that doesn't mean she meant the same thing. There is no way to know what she meant. So you have to either accept the answer you get from her or you don't . But you don't that means you don't trust her and maybe the relationship is not based on trust and honesty.
If this is helpful press accept