iMessage read reports change from read to delivered

In the last couple of weeks I've noticed that when I send an iMessage from my iPhone 6 to my best friend, it first shows as delivered, as usual. She then reads it and it'll show as read. Then I'll go back into message later and it's turned back to delivered again, as tho the imessage hasn't been read at all.

Does anybody have an idea as to why its doing this?? Or what I can do to correct this???

Thank's in advance!!