You need to talk to the temp agency you hired her through, but it is my understanding that the agency would perform all of the employer responsibilities. You however need to make sure they are doing so.
You need to be careful under certain benefit plans. Even though they may be a temp, it is possible that they would become eligible for a plan...such as the 401k plan depending on how it was setup. You need to make sure those plans specifically deal with temps and their eligibility as a class/group. If your plans are silent, it could become an issue if they work longer than a certain amount of time.
Many companies have a strict policy on how many days a temp can exist before they either get hired as permanent employee or traded out for another temp for the reasons I stated above.