If she's carrying eggs already then you should NOT use the diet at that time...that's why I recommend starting after she lays an infertile clutch and don't mate her while she's on the diet.
With a female veiled or panther if you overfeed them constantly or even a lot they will produce large clutches and it can lead them towards MBD, eggbinding, follicular stasis, prolapse, etc...so by putting them on a "diet" that will make them produce smaller clutches or even no eggs at all is a good thing IMHO as long as it's done right so it doesn't cause other health issues.