She may not be ready to lay yet, some birds take longer than others to mature enough to lay. 25 weeks is still young. Normally their combs will brighten and redden as they get closer to laying. Even mature birds that go out of lay for molt or for the short days of winter will again have paler combs until they come back into lay. If you are concerned about parasites then getting a fecal test done to check for them would be best. Some vets will do for chickens some will not, there are also mail in options:
https://www.amazon.com/dp/B000J5SOZ4/?tag=backy-20
If parasites are found then using the appropriate wormer for that particular parasite would be best, medications and doses can be different for different parasites.
DE is completely ineffective as a treatment for internal parasites, and can cause respiratory irritation, so I personally would discontinue that. If external parasites are an issue then a product containing permethrin is most commonly used and much more effective. Elector PSP is also good but is much more expensive.
https://the-chicken-chick.com/poultry-lice-and-mites-identification/