All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no evidence of the permissibility for a woman in menses to perform ablution. It is for this reason that the jurists stated that it is not desirable for a woman in menses to perform ablution when going to bed and when eating whereas this is desirable for a person in a state of sexual impurity. This is because the state of impurity of a woman in menses lasts for a long time.
Rather, some scholars stated that she is sinful if by performing ablution she intends to become pure because this is not correct.
However, if blood stops from a menstruating woman, she is considered as a woman in a state of sexual defilement, and in this case, it is desirable for her to perform ablution when going to bed as stated by the scholars.
Therefore, it is not desirable for a woman in menses to perform ablution when going to bed unless her menses stop.
It is confirmed in the Sunnah that when a person is ill, the reward of the actions that he used to do when he was in a state of good health will be written for him. We hope that the same thing applies to a woman in menses and she will be rewarded during her menses because she always maintains herself in a state of ablution.
Allaah Knows best.