Dewey immediately accepts Della as their mother whereas Louie and Huey had to warm up to her at first. This is because he's met her before, during the trip back in time on Christmas. Thus when he saw how Della acts he instantly knew it was her.
Della's knowledge of the staff (or lack thereof) seems to indicate she really was a Jack of All Trades for Scrooge growing up. She was tough enough to fill Beakley's original role as a bodyguard, she was the pilot Launchpad filled the role for afterwards, and she was the combination of all her sons that she managed to back Scrooge up well on adventures with little trouble.
Launchpad had not become Scrooge's pilot until the start of the series, 10 years after Della disappeared. During the first episode he can be constantly heard talking about being a pilot (or at least wanting to) with Scrooge ignoring him. With the reveal that Della used to be the pilot of the Sunchaser, it means Scrooge likely grounded the thing because he couldn't deal with the memories.
The Cartographer's Quill leads the user to great treasure. Scrooge uses it, and barely a moment afterwards, he finds the greatest treasure he ever dreamed of: his niece Della, alive and here.
It turns out Della might have had a pretty good insight as to how her boys would turn out, as her original names for Huey, Dewey and Louie are actually fairly reflective of their characters; Obviously, 'Turbo' fits someonelikeDewey very nicely, Louie AKA 'Rebel' tends to brace against Scrooge's authority and lessons to the point of actually looking to one of his enemies (Goldie) as a potential mentor, and 'Jet', a highly complex, powerful machine that nonetheless falls apart in the wrong circumstances is at least somewhat reflective of Huey.
When Della reveals her intended names for her kids, she's aghast that Donald didn't use them since, not only did she tell him, she wrote it down in case no one could understand him. This indicates she was at least prepared for the possibility that she wouldn't be there to give them their names herself. While she surely didn't expect to spend eleven years trapped on the moon, and it doesn't justify being willing to take the risk in the first place, someone who faces possible death on such a regular basis does need to be prepared for the possibility and have some sort of contingency for the ones they might leave behind. On the other hand, since this is the only hint of a plan for her children's future, it reinforces that she's impulsive and doesn't think things through (at least before her character development).
The Fizzy Rocks that Della uses in her cake, and which Dewey hasn't seen for a long time, have probably been sitting around for years. This may have contributed to some of the effects seen after Dewey eats the Firework Cake.
Scrooge kept some of Della's clothes on hand - or even had a whole new outfit ready - for when she came back. (And looking closely, she replaces her goggles too.)
Fizzy Rocks were the subject of a lot of lawsuits, and the government eventually declared them unsafe to eat. Where and how does Della, after ten years on the moon, buy some?
She doesn't need to buy any, she likely had a stash of them in the mansion.
