They needed to be physically present to vote. Remember McCain and Kennedy respectively showing up?

As to committee hearings, they have some options. They can watch live coverage of any open hearings and have staffers there. If they were watching and had a question not asked, they could get a message to a staffer and a peer could ask the question. Her office would continue to work for constituents.

As to nursing, she has a private office with a door. She is in a far better situation than most working moms. As to nursing on the floor of the Senate, it doesn't make sense. If you ever visited the Senate, you would know Senators don't often sit there other than right before they speak. They can watch from their office via CSPAN.