I was in a supermarket recently with ds (age 5, really should know better). It's a small, local supermarket, with no public facilities.
Just as I was paying, he said he needed the loo, now
I told him we'd be home in 2 minutes, all fine, etc etc (would have taken longer to walk to a loo in town than drive home). And then the customer service lady took pity on him (we regularly have a chat, so she 'knows' me) and took us through to the staff toilets. I was surprised she did, as I hadn't even bothered to ask, expecting H&S, insurance issues, etc.
We obviously had to be accompanied at all times, but ds was very grateful. But it isn't something I'd expect any staff member to do, and I certainly wouldn't ask - didn't when pregnant (x3, yes I do know how urgent the need to wee can be sometimes), even when I desperately needed a bathroom (hyperemesis x3, so regularly vomiting too - my pregnancies were such fun!). You can't ask or expect someone to put their job on the line, go against policy, and break all kinds of safeguarding issues, however pregnant you are.
Be cross that there aren't more public toilets.
Be frustrated that late pregnancy is the pits
But don't be angry at someone just trying to stick to company policy.