For adult players, I think you would find a complete range of reactions. Some clubs / players wouldn't bat an eye, others would find it an amazing thing to happen. Most clubs have open space showers for players, with no 'modesty curtains' and players shower naked.
As a young female referee in a Society here, you would be very carefully chaperoned and separate changing / showering facilities provided for you. I recall one Hampshire L8 cub brought in a caravan for a visiting London exhange female referee to use for changing / shower.
I do know a Hampshire referee who accidentally walked into the Alton Ladies showers when he did a Premiership match there in the late 1990s - he was 'kidnapped' in there and photos were taken - nude showering was standard for the girls.
Back to the serious side of this issue.
For younger players things are different in NZ (and USA) to England. We have quite strict national and RFU Child Protection / Safeguarding policies and legislation, so your situation would not arise, or if it did then complaints could be made if you joined the players in a shower. In England, club and school players U18 and younger usually shower in underpants, boxers, cycle shorts etc.
There are still a few clubs / schools with no or poor changing facilities, some have no separate refs room and fewer have separate officials showers. But it is better than a decade ago and most new facilities built tend to have a separate refs room with en-suite shower / toilet.
In England a match official of 16 yrs or older must have a CRB (Crimminal Records Bureau) clearance certificate to be able to officiate. If 18 yrs or older then there is no way that they can share changing, or certainly showering facilities, with any players under 18 years old.
If you did as an 18 yr old referee shower with same or different sex Under 18s and it was reported and went through to the Club or CB Safeguarding Officer, you could be suspended immediately by the RFU through the CB - the Society would have no say in the matter, or any other Child Safeguarding allegations, where you are guilty until proved innocent. If your job involved CRB clearance (e.g. teacher) it is likely you would be suspended from work too. That would all apply until your case was brought and heard (could be months later). The official approach is somewhat draconian in some areas, so often such "indiscretions" are dealt with unofficially and kept away from the Safeguarding Officers.
