Actually, this is a very good rule at whatever stage of your career you are. But when the relationship is new, it pays to be doubly aware.
No boss is going to be happy being presented with bad news. The one thing worse than that is unexpected bad news. If they will be called by an unhappy client, it helps them to be able to prepare. They may be able to minimise other problems if they know soon enough.
This is not to say that you should run off to the boss every time there is the slightest glitch (which suggests that you are unsure of yourself). And if you are able to say “and this is what I am going to do about it” when you raise an issue it always helps.
There is such a thing as “Junior Partner Syndrome”, which is seen when a junior partner leaves and the firm discovers a series of writs from disgruntled clients in their desk drawer. Do not catch it.
Strangely, raising problems at the appropriate time can actually increase trust and confidence, rather than decrease it. If your boss knows that she can trust you to bring problems to her at the right time, she will have less need to supervise closely.