Translation:She has nineteen coats and wants another one.
'She has nineteen coats and she wants another' was marked wrong but I think it should be accepted
I have added translations using the second "s/he." It's not needed, but it's not wrong to use it.
There are many acceptable translations that use "he." There is no current report, however, so we cannot tell you what may have been wrong with your sentence. Or you may have run into the occasional grading bug...
"She has nineteen coats and wants another" is accepted. If that was your exact answer, you may have run into the intermittent grading bug. But since there is no report in the system, we can't say for sure.