Can federal judges be impeached?
Yes, but the standard is the same as for a POTUS, as far as charges go, iirc.
Besides the case alleges email leaks. She may have sold the information instead, or even bartered or given it away. If she was having 'secure' communications with an enemy of the US, it may not have been a violation of security, but intentional communication instead.
That opens many other avenues of approach and other cans of worms, but they'lll be glossed over, just wait.