this girl hates me for no reason and I am very confused

I'm in high school right now and last year my friend started talking to this girl. she told us how nice she was and fun to be around so she started talking to the rest of my friend group too, but she never looked at me or even acknowledged me unless I was directly talking to her. I didn't think much of it so I just ignored it but this week I find out that she literally invited every single one of my friends to a dinner except for me, even one of the girls she talked to as many times as me. All I have ever done is be nice to her while not making it seem like I desperately needed her to like me. I have no idea what I did to offend her and I don't think my friends noticed her behaviour either, so I am just very confused and I'm unsure how to bring up the topic because they seem to like her. I really really need help and it has honestly taken a toll on my mental health :,)