____of the four sisters, is Head of Emergency Nursing at the local hospital.
When you are comparing more than two things, you use the superlative with the -est ending. If there were only two sisters, Jane would be the older because comparisons between two things get the comparative form that ends in -er. [Hint: look at the number of letters in the suffix. If there are two, it's a comparison between two things ("He is older than she."); if there are three letters, it's a comparison among three or more things ("He is the oldest of the five brothers.").]