When Kristin was 3 she was tested for precocious puberty and the tests were not conclusive and we did not treat.  She has some body odor and a few pubic hairs.  When she was 5, not much had changed except the beginning of breast buds.  We tested again and she was definitely into puberty.  The endo said it probably was back when she was 3, but the test was not definitive.  It sounds like the signs are there with Samantha and I would ask for the test for puberty.  If it comes up negative, there is not harm in having had the test.  If it is positive, you can choose a treatment program and get it under control before it gets worse.