Women only toilets?

Is it a requirement to have a separate toilet for women? Our PM hired me a few labourers to help clean up before scaffolding tear down. One of them was a woman. A couple hours ago she came up to me asking where the toilet was. I pointed to the porta-johns by the site office. She said "no those are the mens, Where's the one for women?" I told her that's all we have and went back to doing paperwork. About a half hour ago I finished my paperwork and went to go check on the workers and she wasn't there. I asked where she was and they told me she left because there was no bathroom for her. I get that's on big sites there's a women's only toilet, but this is a small site. There's only 4 guys from out company and occasionally subs and labourers. One of the sparkies is a woman and she's never complained and we've had a different female labourer that also didn't say anything. And this one apparently can just walk off site with no word. If I hadn't checked, I probably would have paid her for the full day, since after giving people tasks, I spend the majority of the day doing paperwork/ordering. I called the labour company and told them what happened, and told them I'm not paying her even for a half day. They apologised and said they wouldn't send her to our company again. In the nearly 10 years I've worked for this company, I've never had an issue. Only once I had a new hire ask about a women's toilet, and when I told her no, she used the same one as everyone else. Is it a requirement to have a separate toilet for women? I know on other sites when there was 3+ women they got them a separate one, but on small sites like these where there is occasionally a woman on site, doesn't warrant having a separate one that will be used only a handful of times.