Notes
Angel is an absolutely incredible healer that, through the Voyage Moments, everyone is not only given for free, but given at five-star. In some ways, she is actually a better dedicated healer than either Luke or Anastasia or Samantha, so she should not be underestimated just because she is an Epic-rarity character.
Angel's trait, [Angel] (what a clever name), is simple: it increases her healing effect by 15% and allows her to provide a random [Level 1 Attribute buff] to any allies targeted by her skills. The buffs themselves aren't very strong, but if you're lucky enough to have a decent number of buffs active on your characters to activate, they can be helpful, and are honestly just nice bonuses on top of the healing they provide.
For a basic attack, I prefer [Dispelling Strike]. In all actuality, it's unlikely you should ever really be using her to attack in any case, but in the rare instance where you might need her to do so, buff removal is more generally useful than a small amount of extra healing on the following turn.
Both of her reaction skills have their uses. [Endurance Activation] is more generally applicable, since Angel should be using her AoE heal almost every turn anyway. The damage reduction from [Protection of Light] is greater, though it only works once per turn. Here's the thing to consider, though: if an enemy times their turn, do you expect Angel to be attacked per turn? I prefer [Protection of Light] because she really shouldn't be getting attacked more than once per turn, anyway. This also can be very handy on some of the Weaponry Trial bosses (where she tends to really shine) which can unleash single-target nukes on turn 1, before she has a chance to fire off a heal to activate her other reaction skill.
[Light of Healing] is Angel's bread-and-butter, and she should be using it most turns. The healing it provides is solid, and the debuff removal is also helpful, and it casts in a 2-tile area around the targeted character. It can be targeted up to 3 tiles away, meaning that it actually has quite a bit of range. This skill also provides an all-with-her-stats giving everyone in it with 3 buffs. If combined with a Reorganized Cube and an Empress Tarot, it can also remove up to 4 debuffs from all targeted allies, meaning it is almost always a relevant skill in any combat situation.
[Flagellant], at first glance, seems like an odd skill for Angel, since she's not a tank or really meant to take too many attacks at all. However, that damage reduction certainly is nice, the real beauty of the skill is that after Angel takes damage for the first time in the fight (including any kind of DoT effect), the skill gains an extra +1 NRG per turn for the rest of the battle. This enables her to use [Light of Healing] every single turn without any downtime at all. As such, for certain fights, it can be helpful to let Angel take a love tap from an enemy or walk over a [Search] tile, etc. in order to give her a stack of [Penance] for the extra NRG per turn.
Her final skill slot can be a bit of a flex slot. Here, I have suggested her [M-Def Command] skill, as it can be very helpful for certain content (such as Weaponry Trial I and III), though it can also be borderline useless for other content (such as Weaponry Trial II, or other physical-heavy battles). As such, feel free to swap it out for either [Healing Spell] or, if you're inclined to use a Castalia on her, [The Protected].
I have mentioned the Weaponry Trials a few times in this guide, which I don't normally do, as Angel is a staple of teams for all three trials, and, as such, you should consider bringing her in your attempts to beat them.
For a weapon, you definitely want a Reorganized Cube for the extra healing effect and, more importantly, debuff removal. For a trinket, there's nothing she particularly needs, so choose one that fits the needs of your specific team and the specific content. I find that Divine Bells is always a safe bet, but Legacy Hat can protect her from burst healing shut down, whereas Old Scrolls of Auguste can be helpful for SPD manipulation on your team. For a tarot, I strongly recommend Empress, as it gives her extra utility and debuff removal, which is great for her AoE healing. For a driving force, I don't see a need for any CD reduction of any kind. If you're running [Flagellant], you can use cup + cup. When rolling stats, aim for M.Atk, since all of her healing scales off of it.
