Translation:She enjoys learning English.
This should either not be an audio exercise, or else 他 should be accepted.
Here, English is 英语, but in a previous example Chinese was 中文. Could English be written as 英文, and if so, what's the difference between 语 and 文 ?
語 (even more so: 話) suggests the spoken language while 文 suggests the written language. So you would 說英語 and 寫英文. However, 說英文 is acceptable.
when writing from hearing it is a bit silly that duolinguo does not recognise 他 and 她 as the same.
The character 她 means she, whereas 他 means he. You can tell because of the female radical (女) on the left side of the character. They are both pronounced "ta1." In speaking, this means 她/她 is more like "they," and doesn't explicitly state gender.