Does the act of the mother, consisting of sprinkling henna and milk in the house—due to her belief that it repels the evil eye and drives away devils—nullify the intention of sacrificing to thank God for His blessings? And is she excused for being uneducated?

What your mother did does not affect your actions, for every soul is accountable for what it has earned, and no bearer of burdens will bear the burden of another. Ignorance is an excuse for one who could not acquire knowledge, but whoever was able to and fell short, then they are sinful.