Not really strange at all. When you call for a line increase a re underwriting occurs. With the new information of a decreased income her risk was greater and she did not qualify for credit.

There is a lot of debate about income as a predictor of risk. It is not part of a fico score for instance and all incomes can have good or bad scores. The regulators take an absolutist view of income. Which they can not even degine whose or what items should be included as income as a key factor insetting credit limits. At some point clearly lack of income will influence bill payment but it really should be up toeahbank to determine their risk appetite.

Moral. If there is a decrease in income it will affect even current cards with on time payments if it is disclosed to the lender.