['It is something that was really important to her, and I still feel bad that I missed her 15th birthday', 'Who is she?', 'My cousin, she really wanted me to attend her party since she enjoys my cooking and I had planned on making cookies']
That is bad. Did you bought her a good present so she can forget about it?
I recall a time when I had to go to my cousin's birthday part, and I overslept! I felt really guilty about that.