Yes, LH has a hard expiry unless you have the M&M credit card. SAS mileage expires four periods after the one in which they were earned (so up to five years until expiration).

The thing is, the great circle distance of a round trip CPH-XXX-DTW (with XXX being FRA, AMS, YYZ or such) is like 8,500 mi at best. With two round-trips per year at the most in low booking classes such as K, L, and T, you're looking at 4,250 award miles p.a. That is when crediting to LH or SK. UA can be a bit better (e.g., when flying in T) or sometimes worse (e.g., an LH ticket in K earns nothing).

In my mind, it is doubtful whether crediting miles at all is worth the trouble. I mean, unless she has other *A flights in additions to the trips home. Probably, I'd just disregard the alliance and look for the best overall deal (price/travel time/hard product/etc). With that flight profile, why purchase a *A ticket if Delta is, say, 10 or 20 percent cheaper?