1. Which part is troubling you? I read it to mean that she can put the money in an envelope, mark the envelope for "Ann Shirley" and give it to anyone working there.
2. It means, more or less, that one did not plan to be doing what they ended up doing. In this case, I would say she did not leave the house with the intention of going grocery shopping, but then decided to do the shopping while she was out.
Student or Learner