So your CEL comes on while engine breaking down a long hill?
I've never heard of a warmup being bad on the cat. The warmup is bad on the DPF not the Catalytic Converter. Excessive idling and city driving will fill up the DPF. If your wife drives 30 miles to/from work at nonstop speeds over 50, warm it up all you want. The DPF will have plenty of opportunities to regen and clean itself out.
I've never heard of a warmup being bad on the cat. The warmup is bad on the DPF not the Catalytic Converter. Excessive idling and city driving will fill up the DPF. If your wife drives 30 miles to/from work at nonstop speeds over 50, warm it up all you want. The DPF will have plenty of opportunities to regen and clean itself out.