My work superior has deleted emails that contain evidence about her wrongdoings from my work email account. Also, emails that support my good work have been deleted. Is there anything I can do about it?
Retroactively, probably not. Some things you might want to try include:
1) Ask your IT department if the emails are backed up somewhere. Depending on the size/scope of your company, it's possible they host their own email server where you can retrieve them from.
2) Ask the people who sent those emails originally to re-send them if they have copies (in their "sent" folder, etc).
Things you can do in future:
1) Back up important things by e.g. sending them to a personal email account or printing them in hard copy. Especially, you wouldn't want to lose track of emails supporting your good work, in case you need them for a future job hunt.
2) Don't let this coworker (or anyone else!) use your account. How did this happen anyway? You should make a practice of locking your computer when you're away, don't let your coworkers do random things on your computer (if they need to do something in particular then they can do what they need, but if they start clicking things they're not supposed to, you should stop them right away).
3) If you believe a coworker is worth building a case of "wrongdoings" against, you should bring that case to that person's manager as soon as you have evidence, and you should continually forward that information to that person's manager. You shouldn't stockpile it, because you may lose your stockpile.
You can be absolutely sure, I think, that emails are never truly deleted from any company server. (The company must always be prepared to respond to a subpoena, etc.)
Having said that – it appears that you are insinuating that you believe that your superior is engaged in "something" that might have "legal, even criminal(?), implications." Therefore I recommend that you discuss the matter with the HR department – (it will be private, of course) – tomorrow morning.
Believe me, you are surrounded by laws and HR policies which protect "whistleblowers." "If you see something, say something."