My Lhasa Apso has a small bump resembling an open pumple. Is she okay?

My 11 year old Lhasa Apso has a small bump that resembles a pimple. It looks like it has a very large open pore and sometimes pus comes out of it. It does bother her when it is touched or squeezed. What could this be and is it detrimental to her health? What can I do to make it go away?