Can birds pass diseases to humans through contact surfaces?

Provided she washes her hands after touching surfaces that came into direct contact with the pigeon, there shouldn't be any relevant health risks from touching this surface.

And just because it sound like the pigeon somehow is nesting WITHIN her apartment: Be aware that pigeons can carry mites that could spread within the apartment and infest plants. I would advise against having wild pigeons in the apartment!

EDIT:

Knowing the pigeon is outside, it's not 100% necessary to remove the nest. It depends on whether this window is used for venting and on the direction of air pressure. (does wind go in or out at this side of the house?). Also it depends on the visual cleanliness of the nest. Bird-droppings can potentially represent a health risk, as they can spread through the air, once they dry out, while potentially containing dangerous micro-organisms. Same with feathers that lie around.

So if wind regularly comes from the side of the nest, she could remove the nest for safety reasons, especially if the window is in the kitchen. Otherwise she can't overcome that guilt by blaming health.