At least one in this thread is smart enogh to keep saving primos.
I tried her in trial and i dislike her style.
I played with simulator a bit and got Childe on roll 30 (i pretend diona is new character in next banner). She came after roll 50.
Knowing my luck, i would probaly get Childe on next 10 rolls in my game and ruin the pity build for Eula.
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If she is out in 3 weeks, you wont have enogh primogems to pull her for sure (if you got Childe).