Rent is ACTUALLY lost in the mail (with a tracking number)

[Matt Faix]

We have a tenant that pays by money order every month, but when she mailed this month's rent it never arrived. She sends it with a tracking number since it's a money order, and we can see that it actually IS lost in the mail this time (went to the wrong post office somehow). 

1. Would you still charge a late fee? She mailed it on the 1st, should have arrived on the 2nd. It is still outstanding and is now the 9th. However, it looks like it truly is the fault of the post office. 

2. Since it's a money order not a check, she would have to get an additional $600 to settle December's rent, which she does not have available. Would you still post notice even if this is an otherwise good tenant that always pays on time?