Marrying a widow as a second wife

I hope respected mufti sb is in best of Imaan and health.This is a very awkward question for me to ask but I am stuck in this dilemma. However I am trying my best not to violate the laws of shariah and Mufti sahebs opinion and advice is very important for me and will inshaAllah aid me in this.Alhumdulillah I am a married man with children and my marriage is running perfect. I have no problem with my wife and we are very happy with each other. Just recently another sister that I’ve got to know has asked me if I can marry her. She is a widow with a child. Now obviously she is someone who has nobody really to help her in certain things which only a husband can do for her and wants to marry. She is also okay and doesn’t mind that I am already married. However I have a few questions regarding this as I do not want to marry her with the intention of helping her and doing a good act then falling into sin. Obviously majority of men wouldn’t mind a second wife but I am perfectly happy not to go ahead with the second marriage if it is or can be islamically incorrect in any way.
The second wife is ready to give up her rights and turn. She says that I do not have to pay anything for her. Anything I do will be from my side without obligation. Is this permissible if it is from her side and she is ready to forsake?