I'm 5'8" and live in a tiny NYC apartment. Our building has 2 elevators though.
Some other possibilities:
1. Citibike share if there are stations near her home and job.
2. Standard bike if there is safe parking in her building. Mine
has one but I don't use it; US$25 per month.
3. Stop by BFold on 13th st. They'll have various models that can be test ridden,
carried, etc. Nice folks to deal with. Bought one bike from them before(2013 Brompton);
getting ready to buy another(2017 Bikefriday Pakit).
Citibike New York City by 1nterceptor, on Flickr