Remote computer cannot hear me on video. I hear them.

I was linked to my sister yesterday and we started a video call. I could hear everything she said, but she couldn't hear me at all. 

All the sound settings seemed to be correct on my side, everything switched on and permissions given? Am I missing something that would allow her to hear me or does something need to be done on her side.

We are both using Dell laptops on Windows 10, and have just downloaded the latest version of Teamviewer.

Thanks in advance