Two Message Conversations for one contact.

Hello,

I have a contact that uses iMessage from her laptop as well as her iPhone. Recently in the past few months I started receiving two message conversations from her, even though I just have the one contact from her. One of the conversations is linked to her email when she uses her iMessage on her laptop, and the other is linked to her cellphone number when she texts from that. I know it's not a problem on my end, as she has this problem with another iPhone user as well. I'm not sure how to fix this, so any help would be greatly appreciated.