Up the stairs with a baby and a carryable stroller is not really safe for mother, baby, or bystanders. She should really have a hand free for a rail, if there's one available.

When I need to use an elevator, I'm usually willing to wait for anyone else who shows urgency. I'm often offered a chance to go first by elderly people, or someone in a wheelchair. I use a sling for one baby, and have the toddler in a stroller.