There's a thing called Common Law Trademark. Once Martina began trying to make money using her image as "Lady Alchemy" she had legal ownership over it.
Registering the trademark gave her addition protection, but it wasn't necessary. Anyone trying to register a trademark for "Lady Alchemy" in a way that might cause brand confusion for Martina would need to do a good faith search of potential Common Law Trademarks before proceeding, and in this case, it's clear that anyone involved in this comic would have been aware of her claim to it.