My brand new Tumi bag was stolen from Hartfield (Atlanta) airport years ago and we flew with Delta. They were not good to deal with, which is why we haven't flown with them since (hopefully this has changed). To get the full amount of compensation for the items in my suitcase I had to submit receipts for everything in the bag. Not an easy task, but I'm always up for a challenge. It was several yrs ago, but I think the amount covered was in the area of $2,000 or $2,500. I honestly can't recall the exact amount (it could have been $1,500). The thing is, any receipts from purchases before she left should do, because they don't know what was in the bag. I didn't buy much when we were in Conyers (we were there for a riding competition) because I had to replace all dd's riding clothes, boots, jackets, etc., which was expensive enough. I do recall that I never spoke to a Delta agent -- all correspondence was by e-mail (they never provided a phone number despite me asking how to call them several times). Also they were super slow to issue my check. Like I mentioned, this was several years ago and things have probably changed since then.
Where is she staying in Europe? She can always ask the hotel concierge to help her track down her bag.
Sorry that she is going through this. Traveling is stressful enough without an airline losing your luggage.