Is the 가 in 키가 the subject particle? Is that why 여자 can only take the topic particle here?
yeah it says it in the lesson, that you put the subject particle on 키 when you are talking about a human/person's height only and then to use the words big/small instead of high and low like when talking about buildings and mountains
She a tall queen
What is the difference between 키가 큽니다 and 높습니다?
Google translate is evil and said that the 키가 option was also correct.
Shouldn't it be woman in general since 는 is used instead of 가?
Technically no. The reason is due to "The" referring to a specific woman and therefore will be 가 .