Room with glass windows as a walls.

Glass walls are rough.  If there's ANY possible way for her to hang acoustic clouds on the ceiling, that would be my suggestion.  You can make them yourself for super cheap or order them from a company like GiK Acoustics.  Minimal issue, just need to cover the holes and paint that part of the ceiling when she moves if she's renting.  Also not sure if every single wall in the room is glass, but if you can get paneling up on any of the NON glass windows, that would be ideal. 

And one more suggestion would be, if she can stomach it, use adhesive or command strips and hang at least a decent size section at first reflection 4-6" thick of the thicker stuff on the window where her first reflection point is.  Or again, buy some panels from GiK for first reflections.  With clouds, and first reflections covered, and if her rear wall is not glass, putting some diffusion on there, would help massively!  Best of luck to you and to her!

@rodman99999 ‘infinitely tuneable’ - +1 : )

I respect that the OP has good intentions as are all the responders, but the situation getting absurd in that a bunch of old men, at least demographically speaking, are advising a young woman on how to decorate her apartment.  Are we next going to give her makeup and clothing advice?

Sometimes it best to let your children figure it out themselves.

I apologize in advance for sounding like an old, cranky guy.

lonemountain

In extremely reflective envrons there seems to be only two solutions, both mentioned here. 1) dampen the hell out of it (heavy curtains like theater curtains- very expensive) , 2) distributed low level nearfield playback

There is an another option. Get Wavetouch audio speakers. Unlike other speakers (more 1st reflection points on walls, floor, and ceiling), walls and a floor influence much less to WT speakers’ sounds.

One must find used WT speakers. I have no time for WT speakers for a long time. Alex/WTA

@onhwy61 very true, it's implied in his post that she doesn't care about these issues