Bereavement is an in-country thing that requires an existing FLR. When successful, the bereaved spouse switches from FLR to ILR. There are no out-of-country provisions for bereaved spouses that deal with it as a circumstance unto itself. You can have a look under Paragraph 317 to see if there's a qualifying sponsor. Beyond that, there's nada.
Getting to extremes, you can also make an appeal directly to the SSHD, or even HM. But the chances of success in these routes are so remote that they are academic anyway.
The general principle in all of this is that the couple lives in the place where their ties are the strongest, and for you that would be the US. The concept makes sense. Short of Paragraph 317, there's really no practical inward route.