She seems to be dying a lot more now, may have to change soon.
Follower stats DO NOT upgrade as they level with you. So your Lydia still has 150 hitpoints, 20 something weapon skills, etc. Once I ran the commands to fix her, she became much stronger.
Please see this thread:
http://www.gamesas.com/index.php?/topic/1285338-folower-stats-do-not-update-with-level-probably-a-bug/
Also on reddit:
http://www.reddit.com/r/skyrim/comments/mkg5v/important_console_command_for_pc_users/