The Lena thing bugged me because she was probably my favorite character. An unpopular opinion here, since she was basically an OC that stole screentime away from Scrooge, but I wanted to see where her story went. She was told some generic fortune cookie bullshit about how she will always be with her and just happily move on.
When Webby found the diary, there could have at least been something in it that showed Lena was an unwilling participant, but there wasn't. The only person who even got a chance to see her remorse was Scrooge, but then Magica absorbed her after Scrooge said he was willing to adopt her. Scrooge didn't seem to bothered by Lena's death, only sending a generic insult before getting sucked into the dime.
Season two can still salvage it. Webby could be properly depressed, since sometimes grief takes a while to set in after something intense happens. Maybe Scrooge will try to console her or something. But if Webby is happy-go-lucky in season two, it's going to feel like the entire narrative arc was pointless.
But I guess we were supposed to be talking about Della. Sorry about that.