I would take the emotion seriously without taking the sentence literally straight away.
In the moment, “I’m never playing again” may simply mean “I feel awful right now”. You do not need to persuade her to love football before you leave the pitch.
Acknowledge it: “That was a really hard game for you.” Then give her space.
Later, when she is calm, see what she actually wants. If she is asking about training by tea time, that tells you the feeling has moved.
I would become more concerned if the quitting comments continue when she is calm, she starts avoiding training, or football is regularly creating anxiety rather than occasional disappointment.
The mistake adults make is either dismissing the comment completely or turning one emotional sentence into a major family meeting.
Listen, wait for the emotion to settle, then look for the pattern over time.
