Catherine Willows left the crime lab in 2012 (eventually running a casino) before returning in 2022, yet the plot hinges on her working as a crime scene investigator in 2019.
While it is possible to obtain a warrant forcing surgical removal of evidence from an individual, one can not be obtained without describing what evidence is sought and by showing a direct link to a crime. Exploratory digging in an individual's hand based on a "it could be" hunch would not be allowed.