Q: Texts received from One Plus One Android sender are not showing up on iMessage

My friend has an One Plus One android, and whenever she sends me texts, I get alerts and they appear in my notification. However, none of her texts appear when I open iMessage. In fact, I can send her texts from iMessage, but after an hour, our text window to each other gets wiped out by itself. Also, the number of her texts remain unread and my notification icon badge doesn't disappear until I completely delete her text window from my iMessage inbox. When I create a New Message in iMessage and I type in her name, instead of name appearing in either blue or green text, it is in grey ( like how e-mails appear).

This just happened randomly a month ago when I still had iOS 8 on my iPhone 6. I just updated to iOS 9.0.1, but problem still persists. This issue only occurs on my iPhone because her messages appear and are received on my iPad just fine. I've tried restarting my iPhone, but that's about all that I've done because I don't know what else to do.  Thanks for your help.