Contact lens, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion.
Colored lenses are considered as part of beauty's parts, that is why it is not permissible in front of the non Mahram men. It makes no difference whether it is prescribed or not. Lenses should not be a part of attraction towards the female.
There is no harm in her wearing tinted lenses. However, she should observe what is required in hijab - that is, modest clothing and behaviour.