That's actually one of the better IV's for her, her strongest build is the combo of sol katti, death blow, wrath, and the brash assault skill, stack it with moonbow and she can be almost as strong as Ayra when under half health acting as a brave user.
@Fantaman
Which banner did you get your Lyndis?
I recently acquired one (+ATK -HP) from the Holy War Banner right before Tempest Trials. Could you imagine my surprise when I saw Brash Assault was a seal.
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes