Is it permissible for my mother's sister by suckling to appear before me without covering her face?

Your mother's sister by suckling is considered your maternal aunt, and it is permanently forbidden for you to marry her. This is because suckling makes unlawful what blood relation makes unlawful. A maternal aunt by blood relation is forbidden by scholarly consensus, based on the Almighty's saying: "Prohibited to you are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your foster-mothers who suckled you, your sisters by suckling, your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in. But if you have not gone in unto them, there is no sin upon you. And [prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful." Therefore, there is no harm in seeing her unveiled.