@Zoe34 You have a lovely loft apartment and, you know the main thing that comes out of your reviews Zoe....people love you, you will be a great host because you have that endearing character that so many hosts don't have!
To the focus of the complaint....That shower is a bit squeezy, and I am afraid that is going to be a re-occuring comment but don't be tempted to hit out at in your review response! As @Linda108 and @Rachael26 have said, thank the guest for their constructive feedback and tell them you are looking at ways to make their next visit a true 5 star experience. That will make you look the star to others who read that review.
If you are going to continue to host for the long term Zoe and are prepared to spend $1,000 or two I would suggest you engage a builder to alter the roof line to make a small 'dormer' gable where the bathroom is! Perhaps even incorporate a small window in it. That would make the bathroom much more spacious, give the shower full height and it would remove the only negative from what is otherwise a lovely listing. You would be able to increase your listing figure by $10 or so per night to, in time, offset the cost of this alteration.
Zoe, don't take this one to heart....you are too good to drop your bundle over what is after all, just a negative perception! This review will slip off your reviews page before you know it, and the only thing that will keep on attraction visitors to it is if you lash out with your response and get into some sort of verbal fist fight.
Let it go and just concentrate on ways you can make yourself even better!
Cheers.....Rob