Hey, I can relate to that too. Writers block, not thinking your work is good enough, being caught between accpetance and living up to your own moral standards. I can relate to all that quite easily. I don't think it's at all INTJ suggestive.
I understand the main difference between INTJ and INTP is that the INTJ is more decisive than the INTP, giving the former the ability to skip the fruitless and engage in the more promising, while the latter gets stuck in almost every place in order to examine it thoroughly before, if at all, making a decision. This difference, I presume, causes the difference we can notice in their behavior: that the INTPs appear to be, and probably even are, indifferent to many things, among them, for instance, what other people think of them, how they come across; whereas the INTJs are quite aware of how they are perceived, resulting, if they care for certain aspects of their public reception, in the construction of an appearance that suits their goals.
So if the carefree attitude of INTPs really stems from not caring about what other people do or think, and the indifferent appearance of INTJs is indeed often a mechanism for self-protection, then I think Daria is better described as an INTJ.
To support my assumption, I offer two of her problems, (a) one about decisiveness and self-protection, and (b) one about public appearance and indifference through contemplation rather than natural development.
(a) In 'Write Where It Hurts', "Mr. O'Neill asks Daria to write a story about people she knows in a dramatic way, but Daria develops writers' block on her project (and resentment for her mother) until Helen urges her to write something that reflects the way Daria wants things to be." (Wikipedia)
The conversation between Daria and Helen:
Daria: My story sucks.
Helen: Well, honey, if you just give it another day or two -
Daria: Everything I do has already been done. I wanted to write something meaningful. I can't write anything at all.
Helen: Maybe you're trying to hard, maybe you don't have to write something meaningful, just something honest.
Daria: I can do honest. I look around me, I describe what I see.
Helen: How about describing what you'd like to see, honestly.
Daria: What do you mean?
Helen: Daria, the easiest thing in the world for you is being honest about what you observe -
Daria: Aaand?
Helen: What's hard for you is being honest about your wishes, about the way you think things should be, not the way they are. You gloss over it with a cynical joke and nobody finds out what you really believe in.
Daria: Aha, so my evil plan is working.
Helen: If you really wanna be honest, be truthful about you'd like to happen. There's the challenge.
Daria: Where the hell did you learn so much about me?
(b) In 'Through A Lens Darkly', "Daria gets contact lenses so she can see better during her driver's test, but rejects them when they cause her physical discomfort. She finds it surprisingly difficult, however, to return to her old appearance." (Wikipedia)
A conversation between Daria and Jane:
Daria: I tell you the truth. This whole thing's got me really confused. I want my glasses back.
Jane: Are you still hung up on that vanity thing?
Daria: That's not it. Everyone already knows I'm vain.
Jane: O, you're one huge narcissist. So if not that, then what?
Daria: This is kind of hard to explain. It's, like, I know my glasses set me apart. When I look in the mirror without them, I can't see a thing. But when I put them on and look in the mirror again, I think -
Jane: Yeah...?
Daria: I think to myself: Nevermind the glasses. You can see things that other people can't. You can see better than other people. So to hell with them and what they think about you and your glasses.
Jane: You're not talking about eyesight anymore, are you?
Daria: No.
