I don't see it being a major issue if the mounting spot is heavy wood or metal, although Direct may refuse to cover free realignments under the protection plan, since it won't be installed to spec. Is this a flat roof? If so, ask the landlord if she would be willing to allow what's called a "Non-penetrating roof mount". Basically it is a metal sled that sits on the roof and is weighted down with concrete blocks. The dish is then mounted to this. It is non permanent and does not damage the roof. The only limitation is that it must be installed on a flat roof, it'll slide off if there's a pitch.
Honestly it's very generous of her to allow roof access at all, since most only allow dishes on exclusive use areas like a balcony or patio.