What time need use?

What correct answer in the first case: worked or has worked? Or other? And why?

Seven years ago, while she (1)has worked part-time in a hospital, Emily became interested in medicine.

Solution 1:

The present perfect ("has worked") is incompatible with temporal "while".

I'm not sure why this is - perhaps because the present perfect locates the temporal focus at the present, (though it locates the events in the past); but "while" locates the temporal focus at that time in the past.

The most natural form for "while" is a continuous form, such as "while she was working", especially if you're going on to talk about an event that happened during that period, as in your example. But the simple past "while she worked" is possible as well.