Hope you are well inshaAllah.
Is there a minimum period of tuhr between Nifaas and Haiz after it? for example, a girl had 30 days of nifaas then finished, had a bath, then before fifteen days were over, saw brownish colour again, so is this nifaas continuing, or istihaazaa, or is haiz started now?!!?
Walaikumussalam w w
Generally speaking, there should be a gap of 15 days between Nifas and Haidh. The aadat will also be considered.
In your situation, is this the first child or have you had other deliveries before?
If first Nifas, then 40 days will be Nifas and after that 15 days tuhr then haidh.
If you have a habit from before and this brown colour is within the 40 day period, eg 36, then this will be her new aadat. If after 40 days, then she will be referred to her previous aadat.