*In my area, a few girls are in Beavers, Cubs and Scouts. They either have separate rooms/tents or share with the Leaders of the same sex, as far as I am aware.
Scouting takes safeguarding very seriously*
In Scouts, under 18s never, ever share tents with leaders. They may occasionally share a large room (ie sleepover in a large hall with no other rooms available) but in this case, there will be separate sleeping areas for young people and leaders, perhaps divided by screens, or pop up tents etc. Every effort is made to ensure that leaders and young people are given separate areas and privacy, and if it's not possible, then that accommodation should not be used.
Mixed accommodation is allowed in scouts, but must always be agreed in conjunction with parents and young people. In practice, it's usual that girls and boys will have separate tents. However, as an example, we recently had a residential where we had only one girl attending (they were cubs, so aged 8-10), and she wanted to share rather than have her own room. We advised parents in advance of this, and asked them to contact us if they had any concerns. We also gave the girl a separate bathroom for changing/washing etc.
The general ethos in Scouts is one of openness and transparency, and taking both the views of parents and young people in to account. Any decisions made must be given a great deal of thought, and also risk assessed.