Entitled? Um...I don't understand why that choice of word. If a writer is working hard to gain an audience, then I don't see the brutality in saying they don't deserve to be read. Of course it has to be worked for...like anything else in life.
Working hard for something also doesn't mean you deserve it. Not when the thing that is being worked for involves other people and their free will. That's the kind of thinking that would say that stalkers deserve the romantic attention of the person they're stalking because they work so hard for it and they put so much time into it and they want it so much. You don't "deserve" their attention/time/money. You can try to earn it, but it has to be freely given, regardless of what you may or may not do to "deserve" it.
As to the choice of my word "entitled", let's look at some definitions.
You used "deserve". That means (according to dictionary.com): to merit, be qualified for, or have a claim to (reward, assistance, punishment, etc.) because of actions, qualities, or situation:
Here's the definition of "entitle": "to give (a person or thing) a title, right, or claim to something; furnish with grounds for laying claim". "Entitle" is a verb, so when we talk about an entitled attitude, we mean that someone either has or feels like they have been given a claim to something. Which is the same as "deserve".
The only real difference in our word choice is that people tend to think of "deserving" as being a positive thing because it implies they actually do have a claim to something whereas saying someone "feels entitled" is only pointing out that they don't actually have a claim to that thing but only feel like they do (and so has a negative connotation, since most people instinctively know that feeling like you have a right to something that you don't is a bad thing).
So, when I say that her entitled feeling contributed to her bitterness, this is basically what I mean: She's put what she considers to be a great deal of time, effort, and mental/emotional work into writing a book. She, like you, feels that this effort entitles her (or causes her to deserve) the attention/recognition/time/money of others ("an audience" as you put it). She didn't get it. Therefore, in her mind, an injustice has been done against her because she was denied what she rightfully earned (again, in her mind, and this is the flaw in her thinking). Thus, she becomes angry about this injustice. The world refused to give her what she thought she'd earned, she is a wronged woman, and she had no real recourse for getting justice (because it's not like you can sue someone for not publishing your book), so all that negativity has just turned to bitterness inside her, and she's chosen to spew it forth for everyone to read.
And that's why thinking that you "deserve" an audience is a poisonous mindset for any author (or anyone, really) to have.