During heavenly tribulations, there cannot be any outside interference. This means, regardless of the danger, nobody can come to the aid of the one having the tribulation.
So, for Klaus to be aided by Maud means it is a violation. However, given the nature of the tribulation and its intensity still the same without any added baggage, it can be said that there was no violation caused by Maud's interference.
This outcome is only possible because of who Maud is. She is the Death's Heart of the True Heir of Death. This means she is literally Klaus's heart, if put in a more ordinary tone.
So while she may be regarded as an outside interference, she can also be considered an aspect of Klaus, so the heavens are not coming against her.
Of course, she is her own person, but as far as the heavens are concerned, she is one with Klaus.
