Judicial immunity doesn't work like that. It protects judges from civil suits, particularly for slander, brought about through the course of their duties, but judges can face criminal charges just like anyone can. If the case against Taft was legally sufficient, there's no way the arraignment judge should have just thrown it out.
When Stabler arrests Karen Campbell he does in fact say she is under arrest for attempted murder, not murder. When he says the word "attempted" he says it quietly, but it's still discernible and the subtitles also say "attempted murder".