I would think that the fact she worked for the FBI is just coincidence as the victims are pretty clearly being selected at random and have nothing in common.
However I think there are two things that are pertinent here.
1. That the point of these attacks is not make all of the people in the metro DC are feel they are not secure. In addition, I think it is pertinent that this is happening in DC and have to ask the question as to how many people who live in this area work for the Federal government. I would assume quite a few. What happens if many of these people stop going to work out of fear.
2. I also find it interesting that giving the choice of targets in this instance, i.e., male or female, which were pretty clearly husband and wife, why did the shooter choose the female. Could it be to demonstrate that we cannot protect our wife's and families? The fact that this particular female worked for the government is just a bonus.