Translation:As soon as she opened her mouth, she began to complain.
I wrote "As soon as she had opened her mouth, she started to complain." This was not accepted, but it should be
On the other hand, the "correction" I received was "As soon as she has opened her mouth, she started to complain." That is not grammatical. It must be "had".
I've reported my answer as correct.
I wouldn't make a huge deal of it; reporting is enough. They are adding translations. Also, if you can prove that present perfect is truly ungrammatical, do so; otherwise you will be ignored. The criteria for adding translations are not burdensome, but nobody is eager to remove translations on a single person's say-so. A reference to a recognized text or a well-reasoned use of ngrams will certainly be considered, although marginal use may still be tolerated in side translations.