Noelle's kit is very similar to Itto's. Her Q converts her def into additional atk and converts her damage to geo. One difference is that even if she is switched off field, the geo infusion will still remain if you switch back into her. The duration is also longer at 15s. Moreover, the aoe of her claymore attacks has larger planar aoe (Itto has larger vertical aoe). Also when she attacks, she can heal the party (with one of her constellations the probability goes up).
On the other hand, her E generates a geo shield. With one of her constellations, after the shield expires it will deal damage with 400% atk scaling. This is Noelle's version of an Ushi nuke. The initial cd is 18s, but this can be reduced with her other abilities.
Her optimal build is very similar to Itto's: 4p opulent dreams, def sands, whiteblind and redhorn are her bis weapons.
Mono geo with Albedo, Yun Jin, Gorou can work. She can also work with Yelan, XQ, Beidou. With 4.2, she gained a new synergy with Focalors. Example team can be: Noelle, Albedo, Gorou, Focalors.
How many NA combos? Full CA spin. C2 increases CA dmg by 15%.
We assume with Q she can reach 4k atk. The Q lasts 15s (4s longer than Itto's) and has 15s cd, giving her 100% uptime.
Xiao, Keqing have base def of 799.3. Noelle, Xinyan have same base def at 798.55.
Perhaps this symbolizes something, like how these characters have a certain connection to the Qing dynasty and the House of Aisin-Gioro. After all, even Noelle (诺艾尔) contains the 'ai' sound in her name. The question is why doesn't Alhaitham have base def of 799? Second point is that Xiao actually has pretty high defense. If Xiao's c4 increased his def and then converted his def to more damage, that would be pretty funny too.
The fact that Keqing and Noelle share the same Korean voice actor also hints that something is going on here.
If Eula reminds one of Euler, then perhaps Noelle may remind some of Noether.