@Takotsubo5, let me give you another hand here: "your" old livejournal is still active. (
link) They don't post there any more, there's nothing tying it to anybody's newer accounts wherever ex gf is now, so if you're her, it should be no issue for you to post proof that you're who you say you are there. It looks like it was made around the same time as your deviantart account so presumably you either still remember the password for it, too, or you know the email you could get a password reset from.
EDIT: Alternatively, you could change the password on that deviantart to something innocuous/impersonal (e.g. 123456 or 'password') and let us know so we could see for ourselves that you have access to the deactivated account, since there's no way to reactivate a deviantart after it's been deactivated for 30 days.
EDIT #2: I found another older livejournal ex-gf said was theirs on an old twitter account. If you can't access that first one, maybe you can still remember the log-in for this one: (
http://mrsmustang.livejournal.com).