There were limits to the Power. The Earthblood could not be used to Command either Despite or the White Gold, so clearly things sourced outside of the Arch of Time were not within its scope.
It seems, however, that ANYTHING within the arch was maleable, including the Law itself. This is what made the Power too dangerous to use - ever.
break the Law of Death by ordering Kevin to destroy Foul? Hile Troy broke the Law of Life by bringing back Hollian,
As for the breaking
Elena broke the Law of Death by Summoning Kevin, not by what she ordered him to do. The Law would have been just as broken no matter who she Summoned, or to what purpose.
The Law of Life was broken to enable Hollian to be resurrected. It was broken by the passion of Sunder, channelled through the Krill*, to release the power of the Forrestal, which in turn was channelled through the Krill to perform the actual ressurrection.
* We have to assume here, that the activation of the Krill was "Sixth Ward" level lore. Why else would the Krill's activation have been the trigger for Amok? If the lore of the Seventh was capable of rending the Law almost without effort, you have to assume the lore of the Sixth would have enabled significant manipulation (and as shown, even breaking) of the Law with sufficient motive of the wielder.