Maybe if it’s doable ?... the feds should charge Tina with something then take her into Federal custody...
Not now - Trump just gave her a federal pardon, remember?
If, as implied, her rights were trod upon, the Feds would have a clear path to open an investigation. They would benefit from Ms. Peters' attorney filing such a complaint. I am not familiar with the details of the case, but I read that Ms. Peters is found guilty of a crime that another woman confessed to.
I cannot explain why the Feds are incapable of finding any grounds to open an investigation into Colorado prosecutorial methods. Perhaps they are not confident of gaining a guilty verdict in that state... they should still try if there is some evidence.