Translation:František is her mom's older brother.
The sentences 'Mám maso pro mámu' and 'Její táta je mladší než její máma' accept 'mother' and 'father'. I haven't come across any other DL course that insists on differentiating between formal and informal terms for parents (e.g. Russian 'мама' always accepts 'mother'), probably in part because the informal English terms can vary considerably with location, and 'mother' itself can also be an informal term of address.
Considering that the creators have accepted 'mother' for 'máma' in more than one sentence, it's probably worth reporting in others.