One doesn't usually leave other names off a first introduction or a 'nametag', as that'd be denying information to the sort of person who knows how to interpret it, but it's fine to call her something shorter, such as Lady Avaricia.
Mercury thermometers can measure up to nine hundred times the difference between the melting point and the boiling point of water. She's not herself worried about their dangerousness but he could do all manipulations remotely with unseen servants if he is. She thinks people've tried almost everything that's cheaper to get than mercury and it's actually just much better; there's not a lot of likelihood they're going to trying at random invent something better. The first thing she'd try to find element-23 would be to ask an alchemist supplier for false-spellsilvers that are acid resistant - is she right that element-23 is acid-resistant, it looks like it ought to be.