Wiping the head when there is henna on the hair or a bag over the henna
Question

If a man or woman put henna on their head and put a wrapper of paper or plastic over it, is it acceptable to wipe over that wrapper that has been placed over the henna? Is wiping over part of it acceptable or is it essential to wipe over all of that wrapper? Can that be compared with wiping over the head cover, because it is difficult to remove it? If a person prays after wiping over that wrapper, is his prayer valid or not, and does he have to repeat it?.
Praise be to Allah.If a man or woman needs to apply henna to the head, then the time for prayer comes and he or she wants to pray without removing the henna, it is permissible to wipe over the henna in wudoo’ but not in ghusl, because wiping over the head is not a strict issue, and the Prophet (blessings and peace of Allah be upon him) wiped over his head cover and over his head when he had applied gum or honey to hold his hair together (mulabbad). 
The same applies if they have put a wrapper of paper and the like over it; they may wipe over it and it is sufficient to wipe over most of the wrapper; it is not essential to wipe over the entire head. 
But it is not appropriate to put the wrapper on so as to be able to wipe over it. 
Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allah have mercy on him) said: The scholars differed as to whether it is permissible for a woman to wipe over her head cover. 
Some of them said that it is not acceptable because Allah, may He be exalted, enjoined wiping the head when He said (interpretation of the meaning): “rub (by passing wet hands over) your heads” [al-Maa’idah 5:6]. If the woman wipes over the head cover, then she has not wiped over her head; rather she has wiped over a barrier, namely the head cover, so it is not permissible. 
Others said that it is permissible, and they drew an analogy between the (woman’s) head cover and the man’s head cover, so the woman’s head cover is like the man’s, and the difficulty (of removing it) is present in both cases. 
Whatever the case, if there is any difficulty involved either because the weather is cold or because it is difficult to do it and wrap it again, then there is nothing wrong with taking a lenient approach in such matters, otherwise it is better not to wipe over the head, as there are no saheeh texts that speak of that. 
If the hair is stuck together with henna, gum or honey, or the like, then it is permissible to wipe over it, because it is proven that when the Prophet (blessings and peace of Allah be upon him) was in ihram, he struck his head together with a sticky substance (an action called talbeed), and what is put on the head in the case of talbeed comes under the same rulings as the head. 
This indicates that there is some lenience with regard to the matter of wiping the head. 
Based on that, if a woman has applied henna to her head and stuck her hair together with it, it is permissible for her to wipe over it, and there is no need for her to undo her hair and wash off the henna. The same applies if she has fastened jewellery to her head. It is permissible for her to wipe over it, because if we say it is permissible to wipe over the head cover, this is more appropriate. 
It may be said that there is a basis for that in the ring, because the Messenger (blessings and peace of Allah be upon him) used to wear a ring yet he did not make the water go between the ring and the skin, so in such matters there may be some shar‘i lenience, especially since the principle with regard to the head is not to purify it by washing but by wiping.  
The man’s head cover, the khuff (leather slipper that covers the ankle) and the woman’s head cover can only be wiped over when purifying oneself from minor impurity (i.e., in wudoo’), not major impurity (i.e., ghusl). The evidence for that the hadeeth of Safwaan ibn ‘Assaal, who said: The Messenger of Allaah (peace and blessings of Allaah be upon him) used to command us, if we were travelling, not to take off our khufoof for three days and nights, except in the case of janaabah, but not in the case of stools, urine or sleep. 
The words “except in the case of janaabah” refer to major impurity. 
“but not in the case of stools, urine or sleep” refer to minor impurity. If a person becomes junub during the period in which it is permissible for him to wipe over the khufoof etc, he should not wipe over them; rather he has to do ghusl, because in the case of major impurity there is nothing that can be wiped overexcept a plaster cast.
End quote from ash-Sharh al-Mumti‘ ‘ala Zaad al-Mustaqni‘, 1/239-242 
And Allah knows best.