Landlords may not require tenants to clean carpets unless the tenant did something untoward or unusual--e.g. pet stains, spilled motor oil, red wine stains, etc. Basically, if the tenant "damaged" the carpet--caused stains or dirt above and beyond normal wear and tear--then the tenant could be required to clean it. However, normal wear and tear is the landlord's responsibility--unless the lease had specifically said that the tenant would clean upon vacating the space. (If the tenant agreed in advance to it, that agreement is enforceable.)However, that said, your daughter should ask herself if, right or wrong, it's worth potentially having a "fight" (e.g. collections attempts; threats  of a lawsuit) over $40 or whether this is a case when discretion may be the better part of valor.