In 5e you usually cannot learn new languages, skills, weapon and armour proficiencies after level one when you level up besides adding some subclasses, feats or multiclassing. Your skills, languages and weapon/armour/tool proficiences are the ones you get on level one (with the exceptions previously mentioned)
The only feasible thing I could see to allow you to use martial weapons with Shadowheart, a trickery cleric of Shar, is to pick the "Weapon Master" feat at level 4 (you have to forfeit an ability upgrade for this but at least you can give shadowheart one point of dexterity so she does not have a penalty) or multiclass her when it´s available.
She is a cleric of Shar and, unlike other classes, clerics chose their subclass at level 1, so it´s fixed when you meet her.
Last edited by _Vic_; 10/10/20 07:37 PM.