What is the Sharia advice for dealing with the whispers of Satan concerning full commitment to the hijab, given the presence of sisters who do not fully commit to it in a non-Muslim country?

The One who commanded the hijab (definition) is Allah, and observing the legitimate hijab is a requirement of your being a servant of Allah. Be patient in forsaking desires and seek Allah's help by asking Him for patience and steadfastness. Read the biographies of the righteous and seek out the company of righteous sisters. And know that one of the greatest means of steadfastness is engaging in calling others to Allah. If you are unable to practice the rituals of religion in disbelieving lands and you are able to emigrate to Muslim lands, then it is obligatory upon you to do so to safeguard your religion.