No, you shouldn't give up on your aunt; God loves her in spite of her rebellion -- and so should you. After all, you don't know what's really going on in her heart; your mother's death may be causing her to think about her own life, and that she isn't ready to die.
Even if your aunt doesn't want to have any contact with you, you can still pray for her and ask God to break through her pride and convict her of her need to turn to Him. Remember: God is able to do what we can't do, and He can work in hidden ways to bring even the most rebellious person to Himself. It doesn't always happen, of course, but that shouldn't keep you from praying for your mother's sister. The Bible says, "The prayer of a righteous man (or woman) is powerful and effective" (James 5:16).
I suggest you also ask God to show you if you can do anything to reach out to your aunt. For example, you might consider writing her a brief note, perhaps enclosing the program from your mother's funeral service and expressing regret that you weren't able to see her there. This might open the door for further contact. Remember the Bible's admonition: "A gentle answer turns away wrath" (Proverbs 15:1).
No matter what happens with your aunt, take time to thank God for your mother and her faith in Christ. And may her example challenge you to live for Him every day.