We have a 2013 Outback with a similar issue of excessive oil consumption that bit us right after we bought it. Subaru offered an extended warranty (8 yrs?) just for that issue. We were excited by their commitment to fix or replace our engine until we found out their definition of "excessive" was >1 qt/1000 miles. Ours started new at ~1qt per 2000 miles and is now close to 1 qt/1000 mi... and past the special warranty. Subaru got away without replacing our engine and we don't get on the highway without carrying spare oil.
These companies are really good at stepping up then stepping sideways.
I agree your friend needs to be more assertive. I'd be going over the service managers' head. Communicate with a paper trail (email or written). The dealer may be getting rewarded for holding warranty claim costs to a minimum. Regardless, the lack of response is part of the problem.
https://ksupport.kiausa.com/ConsumerAffairs