One thing you can do is call the post office and find out from them where the item is. I've had a few packages that I have tracked and it didn't tell me correct information so I called the post office and they were able to better tell me where the package was.
I usually check my tracking on my shipments every day (try to) to make sure it is getting to where it is suppose to, I don't really trust shipping, so I have to keep up on them.
Sending her another order expedited would be one way to handle it and with the few extra goodies to say I'm sorry this has happened would be a nice gesture, even though it's not your fault. Most people know things like this can happen and it does, one way to better avoid this situation is to (if time allows) check the tracking on your shipments and notify the customer if there is a problem during shipping, I had to do it for a Christmas present, the customer was informed it may be late and that I was calling the post office to find out more information, luckily the package arrived just before Christmas and my customer was very happy, also thanked me for informing her of the problem.
Hope this helps :)