Understanding 勝手

Question

Maruko has been told that she can't have the food she wants, and replies:

「いいじゃん別にっ。 いつか食べられる日を夢見るくらい、まる子の勝手でしょ。」
????. To the extent of dreaming of a day, some day, when I can eat (it), Maruko's ??? is.

I can't find a dictionary definition for 勝手 that makes sense here. The best fit seems to be "circumstances" i.e.

"My (Maruko's) circumstances are such that I dream of a day when I can eat it.",

If my translation is correct then it sounds very dramatic/formal in English. What nuance is this sentence structure adding over the more simple:

いつか食べられる日を夢見る

I'd also be grateful if you could tell me what いいじゃん別に means.

Answer 1

I would translate “いいじゃん別に。いつか食べられる日を夢見るくらい、まる子の勝手でしょ” to “It’s none of your business. Leave it to me (Maruko) how I dream of the day's coming when I can eat it to the full.”

勝手 means freedom of doing something. Here it means “It’s all up to me." We often tell an uncontrollable person “勝手にしろ – Do whatever you want! I don’t care a bit.”

Answer 2

This dictionary entry fits perfectly:

［名・形動］

１ 他人のことはかまわないで、自分だけに都合がよいように振る舞うこと。また、そのさま。「そんな―は許さない」「―なことを言うな」「―に使っては困る」「―にしろ」

Essentially, doing whatever one wants; not caring about what other people think.

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Here's my take on the translation:

いいじゃん別にっ。 いつか食べられる日を夢見るくらい、まる子の勝手でしょ。

What do you care? I can dream about eating it however much I want.

Although, my phrasing, especially "what do you care", can sound a bit confrontational. You might want to phrase it more like: "what's the big deal" or "it's fine though, isn't it?" Similarly, adding "can't I?" to the end of the second sentence might make it less definitive and softer.