I don't have statistics about this issue, but I think you shouldn't be afraid.. Some Lebanese may give a female domestic worker an over work "sometimes" but NOT victimize her. Eventually, there is an organization that defends Female rights in general (especially brides and domestic workers), this organization is very very effective currently, you can have a contact with even before you come:
kafa.org.lb
Facebook: KAFA (enough) Violence & Exploitation
Welcome to Lebanon dear