Of course, there may have been more than one Susan, but on March 26, 1663 http://www.pepysdiary.com/diary/1663/03/26/ Pepys pays off a Susan so he has room for the new cookmaid. Perhaps she found local rooms and came back part-time as needed? By the sound of the most recent wash days that would be a good time for her to be around ...
I think there was only one Susan Sarah :)
When she leaves the second time on 24th May 1663,, Sam comments "it seems Susan ... is since she went from me taught to drink," - a reference to her previous employment. When she returns for the third - and last - time, Sam records "Susan beginning to have her drunken tricks, and put us in mind of her old faults".
Chart showing the number of references in each month of the diary’s entries.