Her period comes regularly but the bleeding stops for half a day or a day at the beginning and end

If a woman
sees menstrual blood she must stop praying and fasting, and if the bleeding
stops during the period it depends: 

1 – If
traces of blood remain, such that if she inserts a piece of cloth or
whatever it comes out with traces of blood, then the period is not regarded
as having ended, and she should still refrain from praying and fasting,
whether that happens at the beginning of the period or at the end. 

2 – If the
bleeding stops altogether, such that if she inserts a piece of cloth it
comes out clean with no traces of blood, then this is the sign that her
period has ended, so she is taahir (pure). She should do ghusl and pray and
fast and do all that women who are taahir do. Then if the bleeding resumes
she should stop again. 

The ruling
that being free of any trace of blood during the time of menses is regarded
as tuhr (purity) is the view of the Maalikis and Hanbalis. 

See
Mataalib Ooli al-‘Nuha, 1/260. 

In the
answer to question no. 37839
we have mentioned the view of the scholars of the Standing Committee: 

If the
menses stops for one day or one night during the time of menses, then she
should do ghusl and pray whatever prayers come when she is taahir, because
Ibn ‘Abbaas said: “If she sees blood that is heavy or copious, she should
not pray, and if she sees the tuhr for a while, she should do ghusl. End
quote. 

Majallat
al-Buhooth al-‘Ilmiyyah (12/102) 

And Allaah
knows best.