Hi Jessica Rose
No, your cousin is not just ace, she is one very rare diamond. By the sounds of it she will make your journey so easy, especially in the initial stages and with her skills she will make it very easy for you.
I sense she did not come over to see your parents but especially to see you, this shows you that she accepts you unconditionally for who you are and to make sure that you were alright.
When you go to Bristol, have the following conversation with her in regards to who you will tell next, if that is what you want to do. In that conversation determine how each individual in your family will accept you if you decide to tell them about yourself.
I left my family and friends, with out telling them what I was going to do and I changed my last name, so they could not find me. However, my family found out and long story short they accepted me unconditionally. What I know now, I should not have changed my last name and doing so now would be more of pain.
However, if it does not go according to plan then as you have alluded to you can change your last name if need be.
Take care and best wishes for the future, you do have a wonderful 'sister'
Kind regards
Sarah B
PS That was a lovely story, thank you for sharing it.