Hi David, welcome to the forum 🙂 No, 6.3 is not high enough to indicate diabetes, and whether it is elevated would depend on when and what she last ate prior to doing the test. Non-diabetic levels can vary between around 3.3 mmol/l to 6.1 mmol/l, but can be slightly higher if you ate within the past 2-3 hours, and how much carbohydrate was in that meal.
The most useful test to do is the waking test, immediately after getting out of bed. A reading of 7.0 or more might indicate a need for further tests at the GP surgery 🙂
However, if she has symptoms then she should still get the GP to investigate as there is a test called the OGTT (Oral Glucose Tolerance Test) that can be done to help clarify things further.