Translation:After retiring, she is going to learn to swim.
Yes, 'dysgu' means both 'to learn' and 'to teach'. The meaning is usually clear from the context though.
Also the noun 'dysgwr' derived from the verb (female form dysgwraig) is always translated as 'learner' since there are seperate nouns for teacher.
We hadn't considered that to be a valid English sentence, but we're happy to add it.
Seems strange that 'after retiring, she will learn to swim' is not accepted!