Erica/Patient Problem? (SPOILERS)
If Sarah is Erica's patient then that means one of her regrets will be not robbing the house when she went back in S3. This would mean Dr. Tom wouldn't get crazy angry at Erica and thus would potentially not go back to view his death and learn to 'live' (Possibly meaning he wouldn't get back together with Amanda and retire?)
At the very least, some of Sarah's regrets are going to affect Dr. Tom's past which in turn will effect Erica's past?
No?