Pictures pease but in my head one large mirror across that whole wall. That is an odd place for a sink with thta tiny counter on one side

Why is the sink at one end of the vanity? What is the rest of the vanity counter used for.

Would someone be using a mirror ONLY if they were directly in front of the sink because a lot of stuff that requires a mirror isn't done over a sink. If you are applying makeup or doing your hair you generally need counter and not a sink for the tools or other items you are using.

I agree that a picture is needed

It's a little hard without photos - but I would initially think a framed mirror that runs the length of the vanity (easy to install, just a plate glass mirror with a frame around it)

Here are photos of the vanity/wall where the mirror will go. A new lighting fixture will be purchased after the mirror.

I think you need a mirror that goes the width of the vanity because otherwise someone who is standing at the counter has no mirror. In my experience people tend to do things needing a mirror NOT over the sink directly.

This is not your configuration exactly but a person would be able to use the mirror more or less wherever they stood.