Yes, your Mom is right. Contact lenses damage the eyes in many regards.
First and foremost, contact lenses, especially colored contact lenses, cause corneal abrasion. That is to say, when you wear contact lenses, they are scraping and abrasing your corneas all the time.
Secondly, there is no blood vessels on your corneas, the nutrition that they need is transmitted through the penetration of aqueous fluid and the capillaries around the eye whites. They can't work without oxygen. However, the contact lenses blocked the oxygen out and many problems like edema, inflammation, infection and bloodshot eyes will occur.
   Last but not the least, there are many bacteria, dust, fungus and dacryolim leftover on contact lenses. When your eyes are dealing with them on the long run, your eyes may develop conjunctivitis, corneal infection and other eye disease.