There are different versions about Dhumavati Devi. Devi Bhagawat Puran says the Dasa Maha vidyas are created by Durga to participate in wars against demons.
In other places she is associated with Sati who appears in ten forms before Siva . In Tantric tests Dhumavathi is described to have arisen from the smoke created when Sati immolated herself.
So it is for us to chose which version we want to believe.
But one thing is certain. Dhumavathi is a very powerful goddess who could relieve from troubles
.Dhumavati is described as a giver of siddhis (supernatural powers), a rescuer from all troubles, and a granter of all desires and rewards, including ultimate knowledge and moksha (salvation). Her worship is also prescribed for those who wish to defeat their foes
Even married couples worship her. Although she has very few dedicated temples, her worship by Tantric ritual continues in private in secluded places like cremation grounds and forests.
Dhumavathi Kavacham if recited eleven times for forty days then ,severe financial troubles will be averted. These days the worship of Dhumavathi is not restricted only to tantrik people.
I heard Pandits suggesting chant of Dhumavathi Kavacham to get rid of any kind of serious troubles.
I hope I am able to convey some information regarding Dhumavathi,who is the seventh mahavidya.
PS; I will continue with the nava durgas after a while. Busy with Krishna worship temple visit since last night. Only my Devi Mahatmyam I updated hurriedly.
Lakshmi