Nuala's office within the labs isn't difficult to find, and it's the only one among them that doesn't, particularly, seem to be a center of work, per se - although that'll become clear only after Elsa opens the door, as Nuala invites her to-- "Please come in," --after the knock.

It's unlikely that she's ever heard of something like an open door policy. She has, instead, a be courteous and don't be removed policy; most people tend to manage with it just fine, at least those that actually encounter Nuala in her Xenogen office. It's a clutter of the paperwork that she and Charles persistently favour, and-- sewing, mainly. Her role in the department is largely ornamental, except for the occasions - rarer, lately - when she becomes useful with the magically-inclined who benefit from a gentler hand than Severus is capable of, but she feels strongly about being available, and so she spends her days there, regardless, staying abreast of what those more directly involved are occupied with and keeping herself busy with needlepoint and the network.