They should apologize.
The company’s probably afraid of lawsuits if someone gets hurt using a cell phone—hence, the “no exception” rule.
Also, they may be afraid of lawsuits if they “discriminate” on behalf of one person or group, but not another (in that case it would be another example of the “zero-tolerance’ inanity).
But, as noted above, she could have been told she’d have an “open break time” anytime a call came through from her son.