It seems that she is not sure what she wants so she is acting like a confuse woman around you or it might be possible that she wants to take things slowly with you unless she feels that she is ready to offer her vagina for you. If your observations are right regarding her behavior then it clearly suggests that she wants an intimate relation with you but there are many factors which may holding her back to take a bold step towards that.
She might be thinking that it is wrong to have sex with her own son, she has a guilt nature, she is afraid of being caught, she might not want to cheat on her husband, her ethics may not allow her to go ahead.
Therefore, what you need to do is keep doing what you are doing to approach her but do not force in anything otherwise you would lose every hope you have in your mind to make her spread her legs for you. I am sure with time she will surrender her body to you. I am not giving you any moral advice here as that thing I would like to leave for others to do.