I would try to find out if anyone she knew got out of prison lately. TB tends to be found in prisons and detention centers because they are not well ventilated. When I worked for the state in the 90s, I worked with two guys who had both worked in the prison system. Once you test positive on a skin test, you will always test positive and both of my co-workers always had to have the chest x-rays every three years to prove they didn't have full blown TB, only the exposure. I had a couple of clients who were also exposed and they had to take 6 months of medication. I don't know if that regime has changed by now. It might have because the article on the day care doesn't mention them having to take it for that long.
They should find out for certain that she did not get it from one of the kids.
This is the kind of thing I worry about happening in day care centers and elsewhere because of the anti-immunization movement.