All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is a well-known difference of opinion on this issue.
The Maaliki School are of the view that it is not obligatory to perform ablution for the one who suffers from any form of continuous incontinence at all.
The view of the Shaafi'i School is that it is obligatory to perform ablution for every obligatory prayer. For example, if a woman prays the present obligatory prayer and then she wanted to make up for another prayer at this time, then she has to perform ablution for this prayer.
The same thing applies to a woman who made an oath to pray any given prayer.
As regards the Nawaafil prayers, then she may perform as much as possible of optional (Nafl) prayers that she wishes at the time of the obligatory prayer.
The Hanafi and Hanbali Schools are of the view that she performs ablution for each obligatory prayer after its prescribed time has started and she prays as many obligatory and optional prayers that she wishes until the time of this prayer ends.
Her ablution is not invalidated unless she intentionally does something that invalidates the state of ablution [such as if she urinates or relieves herself] or that the time of the prayer elapses.
This is the view that we adopt here in Islamweb.
Based on this view, whenever the time of the prayer starts, she has to perform ablution. But when she performs ablution, she does not intend to come out of the state of Hadath (state of not having ablution); rather, she intends to make the prayer permissible for her.
Also, she does not need to specify the intention of the obligatory prayer for which she performs ablution.
Ar-Rawd al-Murabba’ reads:
"A person intends from his state of not being in a condition of ablution to make the prayer permissible for him [i.e. he intents this when he performs ablution]; by this, his state of not being in state of ablution is removed, and he does not need to specify his intention for an obligatory prayer."
For more benefit, please refer to Fataawa 290107, 330445, 358234, 82085, 345745 and 380429.
Allah knows best.