Me and my friend were playing by ourselves in our own room and I would type things and they could see it, but when they replied through the chat I couldn't see anything they'd typed on my screen at all.
I only know this happened because we were also talking on messenger.
It was through regular chat and not whispers, I didn't have anything off as far as chat goes.
I'm just wondering what happened. We played for at least half an hour and they replied to what I was saying multiple times, but it never showed up on my screen.

Check your settings and make sure that "Show chat from other communities" is enabled

Would that really have anything to do with it? I've had it unticked before(pretty much every time) and we've both been able to talk to eachother just fine. We were in English 2 in one of our usual rooms and everything.

Ask your friend to relog, she may have had a silent mute placed on her. Otherwise, I'm unsure. :(