Why can't I recieve group messages from others on my iPad?

My friend who has an iPhone started a group chat and included my iPad contact into it because I usually text her off of the iMessage on it because I don't have an iPhone. My other friends have previously made a group chat before and and all of these friends that were involved in it have iPhones. So I do receive group messages on my iPad. The problem is that my friend who started the group chat that I mentioned before put more people into a group chat some of which I don't have as contacts on my iPad and two of which don't have iPhones. She added my iPad into the group chat but I didn't receive it on my iPad. She tried it again and still nothing. This is very frustrating please help!