Shalom in Yeshua Teagan, welcome to the forum. I am sorry to hear about the death of you great aunt. The emphasis on GREAT. What a wonderful woman she is!!
When we loose someone we love we all have a tendency to feel guilty about something or other. Its the what if....feeling, which then leads to guilt. Please try not to think this way it is not helpful. You clearly loved her and she clearly loved you. Do you honestly think that she will be annoyed or upset with you for not being there? Of course not.
What you need to do if focus on the happy times you shared, and talk about her to your family and friends, especially your mum. By talking about her you will rejoice in her life and start to forget the pain of her passing.
Talk to her. She can still hear you. She will be praying for you to stop torturing yourself as she is in a much better place now free from pain and in the company of her departed loved ones. She still loves you and that will never end.
May God bless you