frozen pipe: heating tape, compressed air?
You obviously have a severe cold zone where the shower is, what's under the shower" You are going to need to get room temperature air flowing in where the piping is before it turns colder and the pipe bursts when your pipe spits open. If there's a space behind the shower where the pipes are for cutting an opening top and bottom of this space to allow circulation through this space will help or if possible a heating run off the hot air duct discharging from under this space with an opening at the ceiling height to let the air flow through can most likely solve it if you leave the fan run all the time. Poorly designed washroom is the problem with no thought or thoughts to taking out or away any cold air zones when building this house is the only issue. Some builders should stick to fishing for a livelyhood not building houses or really bad designs followed behind by paid off inspectors and the end is always the same, new home buyers need to invest a pile of cash to repair their new houses.