Translation:My older sister is taking a shower.
The prompt said "sister" for あね so I tried and it worked so I'm not complaining. Just curious if anyone else had issues with it being inconsistent on whether the sister's age is important. I think in this case, the question accepts both "sister" or "older sister" but previous questions did not (accept "sister"). Perhaps this is an artifact of the later levels being a mirror of the JA->JA course where あね and いもうと are both translations of "sister".
In the older lessons they were teaching you older sister and younger sister, so you had to specify which one. Now they are just talking about a generic sister, so it's not as important to include the "older". They can't mark it incorrect if you leave out the "older" part, because your older sister is still just your sister, technically, so just saying "sister" will be sufficient.
It's the "てい" in "あびています" that makes it the present tense (..."is taking a shower") as opposed to the future tense (..."will take a shower").
If I wanted to say "I am (in the process of) eating", it'd be "たべています", whereas, if I wanted to say "I will (in the future) eat", it'd be "たべます" without the "てい" in the middle.