Does insulting a girl in a private message, and mentioning that she is "unrighteous" and slandering her honor, constitute slander that necessitates the prescribed punishment (Hadd)?

Slandering a chaste woman is a grave sin and necessitates a legal punishment (hadd), based on the Almighty's saying: (And those who accuse chaste women and then do not produce four witnesses - lash them with eighty lashes) and the Prophet's (PBUH) saying: (And slandering chaste, innocent, believing women). The hadd becomes obligatory upon the fulfillment of nine conditions: four in the slanderer (being an adult, sane, and acting voluntarily), and five in the slandered person (being free, Muslim, sane, chaste from adultery, and of an age where such acts are common for them). It is not a condition for the slander to be public, and it is proven by confession or the testimony of two witnesses. Slander can occur through writing, even in a private message. What is obligatory is repentance and seeking forgiveness from the wronged person.