Is enjoining good and forbidding evil obligatory, and is one sinful if she sees an evil and does not forbid its doer, fearing to alienate him due to her poor approach?

Enjoining what is right and forbidding what is wrong is an obligation upon every Muslim according to their ability and knowledge. Muslim narrated from Abu Hurayrah that the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he is unable to do so, then with his tongue; and if he is unable to do so, then with his heart — and that is the weakest of faith." There is no sin upon one who cannot denounce with their hand or tongue, but denunciation with the heart is obligatory. What you imagine regarding your approach being unsuitable might be a whisper from Satan to discourage you, so strive to denounce with kindness and beautiful admonition. What is required of you is to enjoin what is right and forbid what is wrong, not the people's response. Allah says: "Indeed, you do not guide whom you like, but Allah guides whom He wills," and "But if they turn away, We have not sent you over them as a guardian; your duty is only to convey." So, if you do what you are able to do, that is what is required, and if you are unable, there is no sin upon you if you denounce with your heart.