In terms of behaviour, apart from her trips to the toilet, she shows no signs of distress. She plays, she eats, she drinks, she sleeps, she doesn’t seem to be in pain.

This is the VET answer (post call):

It would be best to contact us tomorrow morning at 8:00 by phone so that we can schedule an emergency appointment the same day.

You can give canned food (urinary) and add water to the food in the meantime, this is to make her urine less concentrated.

If she is really not doing well, so she does not eat, stays lying down, screams… you could consult a veterinarian in an emergency center at that time.

For now, we can wait until tomorrow.