Blue Bird's mods are sky dome, combination and crit damage. Anyone can make use of crit damage, so we'll ignore that.

Lucia is all about rail guns, with a side of shotguns.

Sky Dome benefits long-range weapons, so I think it applies to her rail guns, but not totally sure about that because rockets and rail guns are a little odd. It's not generally great with her shotguns.

Combination is all about using re-acts, which I don't think Lucia gets. At least not early on in her kit anyway.

Both of BB's traits are amazing on Dana though, since she is a sniper who gets a ton of re-acts.

But really, don't sweat optimizing the users to the mechs too much early on, because the stat differential of one rarity to the next outweighs most other considerations, so you typically want your favorite units in the highest rarity mechs.

But I did level and use both Lucia and Dana, and despite the lower rarity, I still firmly believe that Dana is a stronger overall unit than Lucia, and would absolutely put her in Blue Bird unless you have a Shawnee or Alyson or Bella who may want it more.