Yes - Countertops is the Search the List category for this - be sure to talk to them about whether you are providing the cut dimensions or if he is supposed to go to sister's place first to measure her instllation.
Bear in mind - different sinks take different size and shape holes, so unless sink is going to the sister's bear that in mind. Plus does the sink hole fit her cabinet - or is your cabinet installer handling that too ?
Also - who is tranporting and installing at your sister's - should that be part of his scope of work too ? Without proper knowledge and support transporting a granite countertop has a very strong risk of breaking it if you DIY, though granted a bathroom one (unless large or double-sink) is usually les riskk than a kitchen countertop just because they are usually smaller.
Also - unless a backsplash is going to come down on top of this at the back, walls are commonly not straight, so the back edge may need to be cut ot fit the wall profile too. And what is being used at sister's for end and backsplash anyway - is yours supposed to be removed and go there for installation too ?
