She had a miscarriage right after the first month and there was bleeding. Is this menstrual blood, postnatal bleeding, or irregular bleeding?

No, if it is the first month, in the first month the child has not formed, the fetus has not formed, so this is not postnatal bleeding, this is not postnatal bleeding.

Rather, if the blood stops, she should perform ghusl and pray. This is not postnatal bleeding.

This is wound blood, this is wound blood, she should wash it.

And pray, it is not considered postnatal bleeding.