It sounds as though your store's manager is being micromanaged or overruled by the Seagull.
Exactly right!
My suggestion would be that your manager has to deal with this. She's in a leadership position, and it's her responsibility to handle matters that are upsetting her patch.
She has worked under her for more than ten years. She is completely cowed by her to the point that she is looking for another job. She's had enough. She has stood up to her occasionally, but she doesn't have the temperament to do that naturally, and nothing has changed anyway. The seagull is not exactly "open" to suggestions or criticism. I cannot imagine taking a firm stand, and then having to interact with her for the rest of the day, and that is the problem with my boss. It is easier to say your piece and leave, or say nothing and hope she leaves soon.
Even the couriers with stock ask "is SHE in?" when they have to deliver to the store room. What does that say 
A rough plan of action could be:
- Get her to discuss the problem with her peers in other stores. If it's a widespread problem then it's a serious shortcoming with her performance. If it's local, then it's a case that she's not letting go of her baby, as you suspect.
Both correct. Other store managers will call us to warm us she is on her way. It is an open problem, but with only two staff in any store at any time, there is no way of having any "standing together".
- Have your manager discuss the matter with the Seagull's superior. An off the record chat could lead to a quiet word with the Seagull asking her to back off.
I inadvertently let slip something the seagull had done that was not viewed well by the person on the end of the phone who I didn't realise was her superior. A comment was made by this person that led me to believe she wasn't thrilled about hearing it, but wasn't surprised. I said no more as I had no clue who it was on the end of the line. My boss later told me it was the seagull's superior. I was extremely pleased with myself. Had I known who I was speaking to I would not have said what I did. The fact I let it slip out was just a happy result .
- Stand up to the Seagull. If she's ranting in front of customers, then make the point that it's not productive. If she's complaining that you're not doing every last thing she requests then make the point that it's not her responsibility.
When I think back to the time two customers and two staff were there whilst she ranted and abused one of her managers on the shop phone, I don't understand why I didn't nudge her and say "not here", but I had only been there a month or two, had only met her twice and was just too shocked to do anything. If it happened now, I WOULD nudge her. The problem is that when someone behaves like her, there is no knowing what she will come out with. She is just as likely to abuse me in front of people (she has stomped about saying "lazy ba$tards, lazy ba$tards" in a store with customers not three metres away, so who knows what she is capable of.)
- If all else fails, put in an official complaint to her superiors. I'm seriously considering this. I have discussed this with my boss too. I suggested she also put in a complaint when she finds another job. Will be discussed further when time permits.
If the head office is aware of a dispute between your store and the Seagull then it's going to be very difficult for her to recommend blanket sanctions.
You mentioned psychiatric issues. Do you know what she's been diagnosed with? Some of it sounds like
Borderline Personality Disorder, which is what my brother's ex-wife suffers with.
If you know the problem then you can probably figure out how to handle it. A number of conditions involve different models of cognition. BPD involves the sufferer seeing the world in very black and white terms; Asperger's syndrome (or other high functioning forms of autism) has a cluster of symptoms, including sensory sensitivity, difficulty reading social cues, and maybe less flexible in how they think.
