Just attach this flexible plastic cover to just behind the shower head (on the pipe). It works by pivoting at the attachment point and covers the entire shower.

When not in use it simply lies against the wall and is barely noticable.

This kit includes the sheeting which can be trimmed to any size, the framework, and attachment equipment.

Now you can have soothing steam for yourself, and your partner can still use the bathroom. It also helps to prevent mildew buildup from people who like steam and so just steam up the entire bathroom instead of just the shower.