If I have durable power of attorney and my mother can still say yes or no to being placed in a facility. Do I need to pursue guardianship?

If you have medical evidence that your mother cannot live as she is now and needs a home, you likely have the authority to do that. You should check with an attorney, however, to be sure, as states vary on some of these laws.
I hope you can do what is right with minimal stress. Take care,
Carol