First send out the email about the loss separate from anything about rearranging duties. It should include any information you have about the funeral or visitation or even if there is a charity they want contributed to but nothing about business. If you don't have those details yet, say you will pass them on as soon as you get them. It doesn't have to be long or terribly emotional however it is disrespectful to discuss business in the same communication. If there are internal people that she normally works closely with who are not on your team, please include them. Do this as soon as you can, it doesn't have to be perfect..(My beloved died on a Friday and I got no communications from anyone at work over the weekend and I was very upset only to find out, on Tuesday, that they had not actually told anyone even though I had specifically requested it. So don't be responsible for causing more harm by not communicating quickly.)
As far as rearranging the workload, set up a meeting to do that. Also allow time in your schedule for the team to attend the funeral. It is critical that you as her manager attend the funeral. It is helpful if everyone else does too. People who want you to know about their grief tend to prefer to have the support of people they work with. Many offices close for the funeral of a child or spouse of an employee or for the funeral of an employee because most people will feel the need to attend.
You will also want to write an email to any customers (internal or external) who are expecting the delivery by Thanksgiving or who usually deal with her on a daily basis. Do this after the meeting to resolve who will do what so you can tell them that the point of contact has changed.
As someone who lost her life partner (Which is horrible but many would consider losing a child as worse), I can tell you that even when she gets back it may be months before she is fully back to her usual standard of performance. Expect her to show signs of grief for at least a year.
@HLGEM Would you inform the external customers of the extent of the tragedy, or simply that they'd suffered a loss?
It would depend on what the person wanted and how closely they work with the external customers. Sometimes, you just say, they had a personal emergency. When Karl died, most of my external customers were told that I was on bereavement leave and that deadlines would be affected. One asked if I could come in and do just this one thing and our account manager (for whom I am forever grateful) said, "What part of bereavement leave did you not get."