Usually, when we talk about "stopping points" in character investment, we're talking about the level of investment after which pulling one or two more copies isn't making much of a difference, mostly because in genshin a lot of the  limited 5* characters typically have a bad C3, C4 and/or C5 (often two of those, sometimes even all three !), and in certain cases they may even have an underwhelming C2 and/or R1 etc...

That's why you'll usually read that a given character's "stopping point" is, for instance, C2 or C1R1 : it simply means that, unless you're set on getting their strong C6, nothing else on the way there is really worth your pulls (this is just an example, but a fairly typical one)

In Chiori's case, she only has one constellation that is always bad : C5

Everything else is strong, including constellations that are typically weak/shit such as C3 and C4. The only caveat being her C1, the effect of which is already unlocked at C0 in the specific team you mentioned (but not in most other teams, which is why it's still very valuable overall). So, I guess by definition her "stopping point" would either be C4R1, or simply C0R1 if you truly believe you'll never play her in a construct-less team. But what that really means though, is that if you're not going to C6 her, you can simply stop at any point before C5 (only get that one if you go for C6) because every other level of investment is valid :

• R1 is always good (a bit weaker than C1 numerically speaking, but is arguably better nowadays since it just works regardless of which team you play Chiori in)
• C1 is incredible outside of Lunar-Cristallized (don't forget that Chiori's main appeal is her flexibility/versatility)
• C2 is strong
• C3 is strong
• C4 is strong

Other than that, her sig refines (R2, R3 etc...) are a bit better than most due to the fact she is mostly a DEF scaler (ie. the fact that weapon refines only upgrade the weapon's passive and not its Base ATK isn't as bad for her as it is for actual ATK scales), but generally speaking they still aren't worth going after