Is what appeared of viscous brown discharge and brown threads after seeing dryness considered menstruation, and are the fasting and prayers of the questioner on the following two days valid?

If a woman sees the sign of purity (tuhur) and performs ghusl, prays, and fasts, then she has fulfilled her obligations. Anything she sees after that, which she doubts to be blood, is, in principle, not menstrual blood, but rather normal brownish discharge.

Her fasting and prayers while seeing this discharge are valid. She must perform istinja' (cleansing) from it and wudu' for prayer. She should ignore whisperings (waswas) and not pay attention to them. If the discharge is continuous, she should perform wudu' for each prayer and pray with that wudu' as many obligatory and supererogatory prayers as she wishes until the time for that prayer exits.