That's very interesting. In my search for answers to her "issue" I found a thread on here about another sussex with same issue, I'll see if I can find it again.
Their curious nature and sweet temperment is so endearing, but yes - Agnes is a PIA too! I'm often heard scolding her saying "it's always you, isn't Aggie?" In the garden, on the patio or the front porch, or slipping out of the pen just before I close the gate, and while I try to chase her back in, 7 other hens leave. I think she's the designated decoy

(quick I'll distract her and y'all make a run for it!)
She's the most nurturing Mama hen, too - yet tough as nails - she gave the Roo a serious chest bump and chased him off for checking out what her kids were eating last week. Oh, life with chickens!