I would like to challenge the medical guardianship that my sister took out in behalf of my mother.

Too late. Your opportunity to object was at the show cause hearing. If you have documented proof that she has neglected her duties, for example: has not seen mom since the court appointment, you report that to the court who appointed her. Your '06 DPOA was nullified by the court order issued on 1/14/2016.

yes i attended court and challenge, at the time of court I did not have a copy of the DPA. I have that copy now. Plus she committed pergury by stating that the DPA was shared responsiblity and it is not. Plus stating that i put my mother life in danger, by approving a medical procedure, which i didnt. And now i have proof of that .

Did you attend the court hearing that awarded your sister medical guardianship? Did you object at that time?

Have things changed since January that make you think your sister is not a suitable guardian? Do you have evidence about this unsuitability?

(I'm not sure what medical guardianship is. Does someone else have financial guardianship?)

A little more of the story might result in better responses for you.