Hindi ka sensitive, mama, that was rude talaga at meron kang right na maramdaman yan! A few of us moms talk about this din, kung paano ang impatience ng iba ay pagsasabing "Ang tagal naman!" instead of just waiting quietly or kung talagang rush, asking politely like you said. Your daughter was taking her time choosing her own notebook, which is such a sweet thing na pinapayagan mo siya na mag-decide, and that girl could've just waited without the commentary. You handled it perfectly by modeling good manners to your kids, and honestly, that's what matters, na nakita nila how you treat people with respect even when others aren't doing the same.