How can u......get ur closest cousin to forgive u for something u both did??

heres what went down ok we went to our grandmas 4 christmas and she gave us 10$ and my cuz was mad b/c thats all she got and we were talking on yahoo and she was telling me y she was mad. i said that how can u be mad shell be 70 years old and my grandma told my cuz that she didnt have the money to rlly get us any thing and she got the older grandkids and her kids and my cuz said that my grandmas a liar and my cuz called me immature and.......... i just need advice so if theres any one out there that can help PLEASE help me and her are rlly rlly close i used 2 go 2 her house every weekend and hang out lyke every day so if theres anyone out there with an exellent heart please help!!!!!!!!!!!!!!