Whiteblind (4* Crafted) or The Bell (4* Gacha)
Whiteblind gives us 24% ATK+DEF at 4 stacks which Noelle can make good use of. The Bell can refund the CD on Noelle?s E which has a really long 24s cd.
Recommended Artifact Set:
Martial Artist (4) or Resolution of Sojourner + Lucky Dog (2+2)
Martial Artist provides 12% increased damage to Normal and Charged attacks, up to 36% after using an elemental skill for 8s. Since Noelle?s charged attack only lasts 5 seconds max, we can take full advantage of this through Breastplate (E) -> Hold LMB.
Alternatively, Resolution of Sojourner provides us with a flat 20% ATK buff and Lucky Dog provides 100 DEF which we can convert.
I recommend using whichever artifacts you have 4* versions of with rolls in + DEF and % Base DEF.
Normal/Charged Attack: Hold LMB for Demacia. (200 stamina to get the full 5 second channel, or 160 stamina at constellation level 2)
Breastplate (E on PC): provides a shield and a % chance on hit party heal that scales off DEF. It also does a respectable amount of damage based on her DEF stat, but you have to be very close to the enemy.
Sweeping Time (Q on PC): does a burst of Geo damage around her, greatly increases her attack range, increases her ATK based on a % of her DEF, and converts her physical damage to Geo.
Devotion (Ascension 2): When Noelle is not on the field, she can provide a shield for party members when their HP < 30%. Scales off DEF at 400%. 1 minute CD.
Nice and Clean (Ascension 4): Reduces CD of Breastplate (E) by 1s on hit (aoe hits = 1). Greatly reduces the CD of E since her charged attack ticks ~2/s + final hit (11 hits / 5s)
Noelle is best used as a swap whenever Breastplate is available. It has a rather long CD at 24s. Since you will be focusing on DEF, her damage without her Q won?t be great. However when her Q is available, to maximize damage you would swap to her, stack the Whiteblind passive (+24% ATK/DEF at Refinement Rank 1), press E then Q and hold LMB. This will do significant AOE damage and should provide respectable healing to your entire party as long as her E shield lasts.
You can also swap to her just to tank hits since she will have higher DEF than your other characters. I do this for some attacks that can be hard to avoid like during wolf phase 2 or dragon phase 1.
She is only 1 of 3 Geo options (others being the MC/Ningguang), so I believe she is DEFinitely worth getting! In terms of exploration, due to the long CD of her E, it will be difficult to do the timed Geo statues without her ult.
TLDR:?Focus on DEF, Swap to Noelle, E + Q + Hold LMB -> swap off