Faris is a good character for a new player since she brings the ability to dispel (a bit niche but absolutely vital for some fights) and puts massive debuffs on enemies.
For elements, crystal color doesn't have anything to do with it. For example Eiko does Holy damage and is a White crystal character. But Kuja also does Holy damage and is a Red crystal character. Faris enchants herself to deal Water damage and also imperils weakness in enemies to Water/Wind/Lightning (her EX and LD attacks deal all 3 forms of elemental damage whereas her S1 and S2 attacks only do water damage).
The way elemental damage works is, there's a number of tiers for elements an enemy can have. They go Absorb (instead of dealing brave damage with attacks of that element, the enemy gains brave), Null (the attack does 0 damage), Heavy Resist (the damage is reduced by 90%), Resist (the damage is reduced by 50%), Normal (the attack deals normal damage) and Weak (the attack deals 150% damage). When you imperil, this lowers the enemy's elemental weakness by 1 step (so Absorb becomes Null, Resist becomes Normal, Normal becomes Weak).
Faris imperils Water/Wind/Lightning so she's generally going to be hitting for elemental weakness and doing more damage. You won't want to take her to fights where enemies aborbs/null/heavy resist Water, but those fights are pretty rare.
One trick is that elemental weakness overrides melee/ranged/magic resist. For example, Faris' attacks are melee and ranged. Let's say you're fighting an enemy that is Null to ranged attacks (that is, they take 0 damage from any ranged attack). Once Faris imperils Water damage to them, instead of hitting for 0 damage with her S2, she's going to be dealing full weakness damage (150%) because the enemy's weak to Water and she's dealing water damage.
Keep an eye out for characters who can enchant the party with an element so that the whole party can bypass melee/ranged/magic weakness. Fujin can do this for wind next month.