Facebook Messenger automatically seen Messages without any delivered or sent icon showing beforehand

My friend’s messenger on iPhone automatically seen messages even she didn’t open it. It wasn’t even showing a delivered or sent status whenever I send a message to her. Just instantly seen messages of whoever will message her. Even right after I press the send button, it already marked as seen. Why is this exactly happening? We already tried reinstalling messenger and even Facebook but it doesn’t fix the problem. Is there a solution for this?