Eugenia is a bona fide airhead. How could she hide the pilfered jewels in her suitcase, just like that? She knew the place would be ransacked by the dismissed staff before they leave, yet she just went to sleep all oblivious. If all the other servants decided to become thieves to compensate for their unpaid salaries, why would they spare Eugenia? When they saw she was all carefree, they would have deduced she already secured her own fortune. It's much easier to steal that than go around the mansion trying to find something small but valuable, while competing with all the other people for it at the same time.
Any person with above room temperature IQ would have hidden the stuff somewhere outside of the mansion. Because there's also a real risk all leaving servants would be checked by authorities to make sure they don't take with them anything that doesn't belong to them. Obviously that didn't happen, but it could have happened easily. So, she would have lost her jewels at that point and faced criminal charges. But if she had hidden the treasure somewhere outside, she could fetch it afterwards. It's not like the place would have had perfect supervision anymore, anyway, since even the noble children would have gone without food for an extended period of time if not for Eugenia. So, she could have easily wandered outdoors without anyone caring one bit about it.
In fact if she was really smart, she would have stolen what she stole and left before the official announcement the servants are dismissed. It would have been reasonable as well because they weren't being paid anymore. Probably the butler and other higher servants already stole all the money earlier. Leaving early would have avoided much trouble, including needing to compete with the other employees, plus there would have been even less eyes on her. But, alas, she wasn't blessed with a good brain.