This is not a law, she said, but an exemption to the law.
If we leave on the 9th of April, her passport will be stamped with an "overstay" but she won't be fined. When we come back, we can then process the non immigrant O visa at our local immigration (change of visa from tourist to non O) since our daughter will receive a new 30-day stamp at the airport when she enters the Kingdom of Thailand.
Children who are technically on an overstay visa but aren't planning to go to the Philippines or any other countries, and wish to process the required visa, they must do so in another country, say for instance, Laos. That's because they don't have a valid stamp on their passports yet to do the said process in their local immigration.
But then again, she added, getting a visa for my daughter before March 20 is better as oppose to just ignoring it.