If I recall correctly her guns were previously owned by Mistbeard (the Pirate King). He may have obtained them from a previous Pirate King who obtained them from yet another previous Pirate King and so on. It could go back far enough to be from an era when they were made more frequently such as the high tech era that erected Dalamud. Due to the nature of the relic quests restoring timeworn relics (at least that's how the BRD one goes and yet the quest giver owns one himself) Gerolt could mention hearing about an ancient looking chest washing up on the shores of La Noscea and have you procure the chest's contents in Reaver Hide. In which you find old, rusted, sludge-covered guns that need to be reforged. They could even tie in Merlwyb to the quest (including her in a cutscene) which could show her doubting your responsibility to handle such weapons and/or saluting you for proving your worthiness of them.
@Kitru: While I'm sure you may have a good idea or point in your post, I regret to inform you that I will be refraining from clicking the "view" button due to your history of hostile comments and tones toward myself and others. I don't appreciate reading that kind of text and have opted to use the forum's blocking feature as of 11-25-2013. I appreciate you taking the time to weigh-in on my idea but wish to remind you that I cannot see what you write.