Well here the scenes I'm guess it to be. They all contain Lina and Serene arguing. Yep kinda weird spoilering text but still... It could be spoilers.... or not... (http://www.gamefaqs.com/portable/gbadvance/file/921257/46447)
Wiese Forest Screen 05 at Chest
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Lina      : Did it just sink more?
Fia       : Maybe we should forget about it.
Serene    : Lina's light. She could do it.
Lina      : No way! You have wings...
            Why don't you try?
Fia       : Please, you two, stop it.
Tree Hollow Screen 1 at Tree
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Lina      : I want it!
Fia       : But, it's too high up to reach.
Lina      : Don't worry! Lina'll shoot it down.
Serene    : What if you miss?
            Why don't I just fly up there and grab it?
Fia       : Lina, are you and Serene at it again?
Cierra    : Really, you two...
Lina      : Ein, can you decide?
Ein       : Who should go?
Royal Tomb Screen 4
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Ein       : Looks like we can get in from here.
Cierra    : I think it's the rear entrance.
Serene    : There are steps ahead, so kids, be careful.
Lina      : Hey! Who're you talking to, Serene?
 
			
			"If it is possible to manipulate this thread, then it will be possible to control everything in the world." -Luminous Arc