She forgot to remove the impurities from her clothes and prayed wearing them
Question

I had some secretion that was streaked with blood, and I purified myself from it, but some of it got onto my underwear, and I forgot to change this underwear, and I prayed. What is the ruling on this prayer, is it valid or invalid?
Praise be to Allah.Your prayer is valid, and you do not have to do anything, because whoever prays with some impurity [on him or his clothing] that he was not aware of, or he was aware of it then he forgot it, his prayer is valid according to the more correct scholarly view. al-Nawawi (may Allah have mercy on him) attributed this view to the majority of scholars and favoured this view. "(Al-Majmu‘  1/163).
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said: If a person forgets that impurity got onto him, and he did not remember until after he said the salaam at the end of the prayer, then he must repeat the prayer according to the author’s view, because he broke one of the conditions of the prayer, which is avoiding impurity, so it is as if he prayed without wudu’, forgetting that he had broken his wudu’.
The same applies if he forgets to wash off the impurity.
The more correct view concerning all these issues is that he does not have to repeat the prayer, whether he forgot [about the impurity] or he forgot to wash it off, or he was unaware that it had got onto him, or he was unaware that it was an impurity, or he was unaware of the ruling, or he was unaware of it before the prayer or after the prayer.
The evidence for that is the important general principle which Allah set out for His slaves, which is mentioned in the verse (interpretation of the meaning):
{Allah does not place on any soul a burden greater than it can bear. For it is what it has earned, and against it is what it has committed. Our Lord, do not hold us accountable if we forget or fall into error} [Al-Baqarah 2:286].
This man who did this haram action was unaware of the ruling or forgot, and Allah has spared him accountability for it, so nothing further is required of him.
There is evidence which specifically addresses this issue, which is that when the Messenger of Allah (blessings and peace of Allah be upon him) prayed wearing shoes on which there was something filthy, and Jibril informed him of that, he did not start the prayer again from the beginning. If this did not render the first part of the prayer invalid, then it should not render the remainder of the prayer invalid."(Ash-Sharh al-Mumti‘  2/232).
And Allah knows best.