How could I help Mom enjoy New York?

She’s only 67 but has rather weak knees so walking a single block is just about the limit for her. Still, even though New York is mostly a walking city, she would love to go the Statue of Liberty, go to the top of the Empire State Building at night, see Times Square and any small part of Central Park. Are there not so expensive ways for me to help her go around New York? I’m wondering if there are wheelchairs for rent there on a daily basis so we can just push her which is the closest thing to walking and enjoying NY that way, roaming the streets. Taking cabs is an option but maybe there are other creative ways to see NYC for a Mom who is not a walker?