"I am going to a café with her."
Translation:Я иду с ней в кафе.
I think that they are trying to use a cafe rather than the cafe to let us know that cafe is not what is being emphasized. I don't know whether this is just a DL convention to make sure that we get practice in placing the aspect we want to emphasize further forward in the sentence, or whether the moderators actually think that is the function of a and the in English usage. In any case, I am finding it very hard to remember the convention, since that is NOT the function I (as a native English speaker) associate with a and the! Maybe with a few more months of study .....
It kind of is... you just don't have to emphasize who's going. Some other questions use first person pronoun, then verb, then indirect object.
Also, with your answer, it would be Мы с ней идём в кафе; essentially saying "We, including her, are going to a cafe" (but I'm not sure why Я с ней идём в кафе is not accepted; the Мы form is)
I think it may be because of some general basic priorities on proper order, and unless clearly indicated, we'd better follow them. Like subject + verb + direct obj + indirect obj + complements (of place, time, ...). I doubt, though, if indirect object should go first by default, before the direct object. Could this be the reason behind forcing the answer to be "я иду с ней в кафе"?
I believe that would be equivalent to the English "She and I are going..." This has a slightly different meaning than "I am going ... with her." It's a very minute difference, but it would require the corresponding word order for an accurate translation. Word placement is very important to emphasis in the Russian language.