[sblock=For Strahd]I'm not one to argue with the DM, but by my interpretation of the spell, any and all mind controlling effects against the warded creature would be surpressed. While the description mentions "caster" below, it doesn't specifically state that the protection only applies against spells. And since the description in the vampire's Supernatural Ability mentions a caster level, I would argue the Magic Circle vrs. Evil does work against her.
url=http://www.d20srd.org/srd/spells/protectionFromEvil.htm]Protection from Evil[/url]
Second, the barrier blocks any attempt to possess the warded creature (by a magic jar attack, for example) or to exercise mental control over the creature (including enchantment (charm) effects and enchantment (compulsion) effects that grant the caster ongoing control over the subject, such as dominate person). The protection does not prevent such effects from targeting the protected creature, but it suppresses the effect for the duration of the protection from evil effect. If the protection from evil effect ends before the effect granting mental control does, the would-be controller would then be able to mentally command the controlled creature. Likewise, the barrier keeps out a possessing life force but does not expel one if it is in place before the spell is cast. This second effect works regardless of alignment.[/sblock]