He ordered one from his "Witches, Warlocks and Wizards" catalog, but there is such a demand for magic mirrors that it is on backorder. :-/
I wondered about the mirror too, but consider that Angelique herself knows quite a bit about witchcraft. Maybe not as much as Nicholas, but she's no slouch in the spell department. She knew how to send Eve back in time, for example, so even though she's a vampire now, she still remembers all her spells.
Perhaps she knows the spell for enchanting the mirror cannot be placed on a second mirror by Nicholas until the first mirror is unhexed or destroyed. (Witches have strange rules.)
Was Nicholas lying to Adam when he said he had no control over human emotions? Angelique certainly did in 1795, judging by the spell she cast on Josette and Jeremiah. Perhaps this is one area of expertise where she tops Nicholas.
They consistenly referred to Eve's time travel as taking place in April of 1795, instead of 1796. That bugs me to no end. Vicki didn't even arrive in 1795 until October, according to Abigail Collins' testimony at her trial. She left around March of 1796.