uno) This sounds like you are firing the office manager and replacing her with her assistant. Is there a substantial pay disparity? You can argue that it was simply cheaper to keep the less senior employee because they would do the same work for less money. Is there a history of work quality problems? In the end, you will need to be able to justify why you kept one and let the other go. Everyone at the EEOC and in the jury box will understand that the Company wishes not to pay two people to do the work of one, but they will also want to know why you chose to keep the one you did and why you chose to release the one you didn't. Having that information down in advance will be helpful to you should this crop up 18 months from now.
dos) If you provide two weeks pay but leave the situation such that the Company is initiating the separation, then she will get unemployment after the wage/time clock runs out (2 weeks in this example). I wouldn't be concerned about unemployment. You're firing someone who hasn't done anything wrong (or, at least, not terminable as of the separation) and that's what UI is there to cover. If you do a release and settlement agreement, you typically pay them substantially more money but convert the involuntary termination into a resignation along with getting an agreement not to sue for all manner of things. I have seen RSAs that stipulate that the company will not respond to any requests for information for the purpose of making a UI determination (meaning the employee's word stands and they will get UI even though they resigned). Again, I wouldn't really worry about that. The main thing is you have one too many bodies and this person lost the lottery and there's no reason to be anything but compassionate about their unfortunate situation, particularly since the sense of fairness and generosity in their head will keep her away from attorney offices.