Unless the long fin spike has somehow been ripped off or damaged your mandarin is a female. Every fish has it's own little personality. Some are bossy, some are shy, and many like my laid back fire goby do not reflect their species general characteristics.
My guess would be, from your pics, since the mandarin is bigger, she is making sure every body else knows she's top fish.
How many days have past since you introduced your mandarin? One thing to try is to rearrange your LR. That way every one has to establish new territories. :happyfish