is "uma" in this sentence different from other instances in previous lessons? "one" and "a" is not interchangeable. it would have close or similar meaning in many cases, but it doesn't mean the same thing.
why is Duolingo suddenly changing the meaning of a word? if you're going to use it in exercises, teach it in the lesson that it was introduced and explain instead of causing more confusion as you repeatedly do.
The lady has a glove should be acceptable since 1) mulher is woman and lady is also woman; 2) uma is one and "a" is "one". A mulher tem uma luva. The woman has a glove. The lady has one glove. The thought spoken in portuguese and the the thought received in english are the same thought. Communication has happened.