Douyara Watashi no Karada wa Kanzen Muteki no you desu ne

On her deathbed, a sickly young girl wishes to be reborn with a strong body that will never succumb to anyone or anything. Lo and behold, her wish is granted! Upon reincarnating into another world as Mary Regalia, she discovers her new body has maxed-out attributes, from physical strength, to defense, and even magic. But wait! That isn't what she really wanted! All she longed for was a normal life...but that's a tall order when you're absolutely invincible! Join Mary as she navigates her new life as a duke's daughter, makes friends of all stripes—including her devoted maid, an irreverent trainee knight, a proud magician girl, and even the prince of the kingdom—fights off terrifying monsters, and maybe even gets mistaken for a knight of legend!

(Source: J-Novel Club)