That’s a subjective assessment and it ignores the fact that Merkel is failing to meet spending goals she agreed to. But even if 40b “is plenty”, Germany’s military readiness is such that it is not currently capable of fulfilling its NATO obligations.
As far as NATO members being apprehensive about what Trump will or will not do…well, they should be apprehensive. But he’s not the only NATO leader who is stressing the alliance: Merkel and Putin are in agreement (diplomacy in action) about building the Nord Stream 2 gas pipeline directly from Russia to Germany, a project vehemently opposed by fellow NATO members Estonia, Czech Republic, Hungary, Latvia, Poland, Slovakia, Romania, Lithuania and Croatia, as well as the United States.
Trump’s unpredictable, WWE style of diplomacy will not at all be helpful in calming the fears of NATO in the upcoming summit, but by her actions and inactions Merkel is doing her fair share in stressing the coalition.