They've been notified, and are doing it vindictively.
She's sleeping in there tonight with her daughters and the heat off.
@Timothy Burns, I would contact code enforcement. If the heat isn't above the legally required temperature they might declare the unit uninhabitable and boot the tenant out until the situation is rectified (which will of course be a day later when they can come back and verify the temperature is back to normal).
I would also call child protective services. The parent choosing to keep the temp at an unsafe temp with children could be a sign of mental health issues and they may need to take the children away to keep them safe.