Meaning of いーじゃん


I am reading 海街 Diary, and I have come across the dialogue below. For context:
The older sister of the female protagonist calls her, and then has a go at her
because her phone was switched off and she needed to get hold of her urgently.

At this point, the female protagonist, taken aback, says:

> いーじゃん別にそれよりなによ～？

I am guessing the meaning is "Why, what's going on?", but I couldn't find the
meaning of いーじゃん anywhere. I think this may be very colloquial.




There are many ways to use いいじゃん, and in a lot of cases the phrase is hard to
render accurately in English. So it's well nigh impossible, in my opinion, to
give an accurate and comprehensive answer to your title question: What's the
meaning of いいじゃん.

Just to sample a few usages of いいじゃん:

> 悲しいなら、泣けばいいじゃん  
>  If you are sad, cry (literally: isn't it good if you cry)

> A: デートに誘われたんだ！  
>  Someone asked me out!
>
> B: いいじゃん！行ってみなよ  
>  Nice! Just go have fun.

Here, you should note the 別に which imparts dismissive undertones especially
when used in conjunction with いいじゃん. The usage is 別にいいじゃん or いいじゃん別に, and the
general idea is unconcern, or impatience, or sometimes even flippancy. "I
don't care." but not so explicit. Literally it's like "It's okay, isn't it?"
Depending on the context, it can go anywhere between "alright!" "I know!" to
"I don't give a damn!" Here I think a simple "Alright!" or "Okay!" would do.

> いーじゃん別にそれよりなによ～？  
>  Alright! By the way what did you need to find me for?

