IF you (or someone under your control--a child; a child's friend who was your guest; some other family member; etc.) drew the graffiti, then the landlord could seek to recover the cost of cleaning it up; in this case, though, to get the money (if you did not pay it voluntarily), the landlord would either have to sue you (and prove your responsibility) or possibly take it  from your security deposit at the end of your tenancy (in which case, you'd have the chance to seek its return, if you disagreed).Or if there is anything in your lease--which is, after all, a contract--which states that you would have to pay for graffiti under certain circumstances AND those circumstances occured, she could fine you.However, unless she can either show you did the damage (and seek to collect as she could for any damage a tenant does) or has some contractual term allowing her to fine or charge you, she cannot simply decide on her own to impose a fine.