YABU, as we don't know the exact reason for the dismissal or what jusrisdiction applies.
Is she claiming illegal discrimination, or that the company is being discriminatory in applying/following its own policies? Has she said it's discrimination on the grounds of sex? As someone else pointed out, it could also fall under protections for family status or even marital status. Is she planning to take legal action, or just venting? If she doesn't have a legitimate claim, it won't go to court, so no need to worry about it.
Sounds like something that would only happen in the US which is just a cesspit for worker’s rights. Generally workers' rights fall under the jusrisdiction of the individual states. In California, for example, working parents can use sick leave to care for a child, and if not entitled to sick leave sick can take unpaid leave. However, there may be other circumstances in this case - for example, if she didn't follow the procedure for reporting her absence, or failed to provide some kind of proof of the child's illness after x days, etc. The Family Medical Leave Act also applies in every state, so someone who can demonstrate legitimate ongoing caring responsibilities which might unexpectedly conflict with work can arrange protection for unexpected time off in advance without disclosing the details to the employer.
RE the suggestion that workers' rights are worse in the USA than anywhere else: I wish you were correct, for non-US workers' sakes, but in many places they are worse.