Hey ,
Even if the picture looks detailed, it is always hard to asses conditions on a image. For a better understanding of what is at play I would always recommend an examination by a professional healthcare practicioner to rule out some conditions.
Different things could be at play. There are drug induced possibilities. But it would be helpfull to know what kind of drugs we are talking about.
There are also many non-drug related causes.
For example, if she experiences some acid reflux, this could cause problems with the mucous membrane of the upper GI tract including mouth and throat. This can cause pain on the tongue, especially while consuming acid foods. Small ulcers on the tongue cuased by the reflux can react.
Oral hygiene, a history of smoking and drinking alcohol can also cause problems in the mucous membranes in the mouth.
Fungal infections can also be at play. They are for example more prevalent in a so called geographical tongue.
In some cases an autoimmune issue can cause problems causing crakcs.
Some nutrient deficiencies (B vitamins and zinc for example) have also been related to cracks on the tongue.
Simply biting on the tongue can also cause damage. In that case the damage would be more on the side of the tongue.
If there is some scare tissue present on the tongue, the upper surface can be damaged which could cause a dry feeling.
These things can be best examined live by someone with the right medical background!