Can we read from a Mushaf that becomes contaminated with najaasah and is then cleaned?
Question

My 10 year old daughter was cycling to her Quran teacher's residence for her regular lesson.
On the way, she was frightened by a dog chasing her.
In panic, she cycled more quickly towards her teacher's house, when, she and the bicycle as well as the Quran fell into the drain.
Part of the Quran was wet from the drain water.
Upon seeing this, the Quran teacher washed off the dirt, and she was able to read from it.
My question is, what is the hukum on such a state of the Quran? Right now, she is still reading from it.
Praise be to Allah.If the dirt that has gotten onto the Mushaf is removed, and there is no offensive odour left, then there is nothing wrong with reading and memorizing from it. 
But if there is a smell or there is some trace of dirt left on it that cannot be removed, there is nothing wrong with burning it and bringing another one, out of respect for the Book of Allah and the wish not to leave any impurity or bad smell on it. 
May Allah reward you with good for your respect towards the Book of your Lord and your asking such a question which is indicative – in sha Allah – of goodness and religious commitment. We ask Allah to make it easy for your daughter to memorize the Qur’aan and act according to it. 
And Allah knows best.