Around 10% of Sadhus are women, they are called Sadhvis, most women become Sadhvi following the death of their husband, so young Sadhvi are rarely seen.

A Sadhvi is a Hindu holy woman, she is dedicated to achieving Moska (liberation) through meditating and contemplating Brahman.

Sadhbi in sanscrit means a woman who renounces material attatchments, living in caves, forests or temples. Sadhvi are generally considered holy, and able to remove karma. This makes them an asset to a community so people make donations to them.
There is also the belief that Sadhvi can cast curses, so there is also a fear of this which should be placated.

Sadhvi are sometimes believed to be forms of goddesses and are honoured as such.
Sadhvi denote the sect which they follow with markings on the forehead. These markings are called Tilak.
Three stripes are worn by devotees of the Saivile Sect (followers of Shiva). This can be accompanies by a red dot, sometimes a trident or a crescent moon is also worn on the design. Devotees of Shiva use sacred ashes for the tilak.

Followers of Vishnu wear two or more vertical lines representing the foot of Vishnu. Sometimes a central line or dot are added. Most Vishnu followers use sandalwood paste for the Tilak.

Folowers of the goddess Devi or Shakti use red turmeric powder. Some Sects make the Tilak on 2, 5, 12 or 32 parts of the body.