WHATSAPP HELP ON ANDROID

Hello everyone
I am wondering why one of my frequent contacts on whatsapp is showing on my MUM’S phone as a suggestion/ contact in whatsapp chats as well as her phone cone contact list?
At some point my mum and I both had whatsapp backing up and syncing, and as my mum’s primary language is not English, I have her gmail account open alongside mine so I can read ot to her any important emails if she doesn’t understand. Is it some sort of backing up issue then?

Any advice would be greatly appreciated!