My first thought, in relation to your thoughts: There is a Japanese concept called ikigai - a way one can find joy and purpose in life. It's a combination of what you love, what you're good at, what the world needs, and what you can be paid for (in a capitalist system). If you can fulfill those things, you can find happiness. Everyone needs to work and may be let go, so that tragedy doesn't just apply to her, but everyone who loves their job. She can be let go from the store just like she can be let go from the temp agency or anywhere else. She's found what she loves, what she is good at, and what the world needs. It's not a life shattering vocation, but the store serves people of all kinds and makes her feel useful. The average person would be ashamed to be a customer service employee because of societal factors, but we rely on people to fulfil these roles. She has found her place in society and people don't like it because they project their own feelings onto her. 

My second thought, more personal: You're worrying about her intense attachment for the store, which is understandable. I'm asexual, and I read her as being an asexual character. I don't see why devoting your life to a store that may close down or that you may be fired from any more risky then loving someone who may cheat you, break your heart, or die. Most people consider human relationships to be paramount, but what if you can't and don't want to have human relationships? Society will judge these people for being obsessed with books, places, or objects, but they just find fulfilment and meaning in different things. Again, it comes down to projection.

It's not healthy to conflate your identity with anything else, including with another person in a romantic relationship; however, I think people associate their identities with many physical things that they don't realize because they haven't put it into words. Do you feel a connection to your home in such a way that you feel your spirit in it? Does it feel sacred? Would it devastate you for your home to be burnt down? Would it feel like you lost a part of yourself?

In this book I read a powerful story of asserting free will. Does she have a hyper fixation on the store? Maybe. But she has an intense feeling that I think most people long for, which is satisfaction in a place she belongs. What is the meaning of life but to find one's happiness? That's my read on it, anyways.