I take this to mean not that bad things won't happen to repentant believers, clearly we see that they do, but, that they will not be without salvation and God's hand. For Jesus suggests that it is not because of their sin that these two calamities happened, yet, repentance would have still been in order; it is always in order.
This peculiar passage does not quote Jesus as saying "your sins are forgiven" as He does so many times. In fact it says that she is loosened from the bounds of Satan. Not all illnesses nor healings are presented this way. We should not assume, we should approach from a preparatory base of prayer and fasting. Many say "why pray" or "why fast". It is precisely because we don't know what is ahead of us and we just can't simply assume that we know.
If connected in context to the rest of the remainder of the chapter we'd see that this astounding kingdom growth is a result of a caregivers' nurturing care towards repentance (even by calamity), the bounds of Satan being identified and loosed, legalism and tradition and religious expectation being loosed, certain adversaries being shamed in their confrontation, and praise of the multitude for what He has done. Not a bad summation of the Gospel...eh?
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3