Welcome to the forum
No, it's not okay!!!!
You don't want ANY substrate at all in a cham cage, and esp a veiled cham.
They will eat it and become impacted.
Also, don't listen to what pet store employees tell you, ask your questions
here first.
They are told to sell customers all kinds of crap they do not need, that's how
they make their money, it's not the animals they sell, it's the supplies
If/ when she is ready to lay eggs, even infertile ones, you will know, and at that
time, need to provide her with a laying box, which can be a mixture of damp potting
soil and sand.
But other then the laying bow, you do not want any substrate which could be swallowed
either by accident, or otherwise.
You need to find out if she is already gravid too.