Is this the title of a light novel?

When do I use あびます and あびています?

It marked me wrong for translating "sister" as 妹（いもうと） instead of 姉（あね）, even though the English sentence didn't specify whether the sister was older or younger. I've reported it (Jan. 5, 2018).

姉(あね)/妹(いもうと)　は/ が　シャワー　を 浴びて(あびて)　います。