I think the metro is the best ( fastest ) way to get to central New Delhi. She will avoid traffic this way. As far as I can see the hotel is very close to the aerocity metro stop.
The metro in New Delhi has carriages exclusively for women and they are generally much less crowded ( as a lot of women use the normal carriages ).
My information about carriages for women is from a trip almost 2 years ago but I can't see it having been changed.