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.
Declaring someone a non-Muslim is one of the most serious chapters that led Al-Khawaarij astray, causing the loss of many lives and damage to property, and the Muslim nation suffered much affliction and impairment as a result.
However, if by the above statement a person means that Islam if free from the sins and acts of disobedience that this woman is committing then this is true. The Prophet, sallallaahu ‘alayhi wa sallam, said that whoever cheats Muslims is not one of them. [Muslim]
There are many other similar Prophetic narrations but they do not mean that this person is not a Muslim, rather the wrongdoing he did is not in accordance to the path and guidance of the Prophet, sallallaahu ‘alayhi wa sallam.
Allaah Knows best.