Hi Julie, welcome to the LOC, I had my is200 for nearly 9 years , always had it serviced by a small back street garage without any problems, ask around local car parts suppliers if they could recommend any good reliable mechanics and I mean mechanics not just fitters there is a big difference between the two ! You could ask local RAC for any reliable workshops, ... If you didn't drive for long or far with the car overheating then it should be ok, check the oil for any water that might have mixed with it ( the oil will be milky ). Check the oil filler cap also for the same thing ,milky substance, if these checks are negative then check the water in the radiator for oil particals , if this is clear then the head gasket is probably ok , you can get any descent garage to do a pressure check on the rad and diagnose the water from the rad for carbon particals which could mean head gasket, these checks at a garage should take no longer than 30mins max....hope this info is handy for you, good luck.....
Allan