No, It is not possible.
GW2 has a trial feature but just not a permanent one. There are trial events (so far there have been 4 since launch, but they seem to be more frequent now-a-days.
Besides that you actually broke the user agreement. Sharing an account is not allowed. The most important reason is that when the people sharing are not being friendly to eachother any more, this often results in account ownership disputes and support can’t verify who actually is the owner off the account cause it are two people. You actually see that on a small scale in your situation where it allready is ‘your girlfriendscharacter’ while it is your account. So she is actually claiming ownership over something that is technically yours. As said she is your girlfriend and your doing things on a friendly base. So its not an issue here. I also dont think support will make a big issue out of the breach of the user agreement. But I hope you understand that such a feature doesnt exist cause there is a difference between not making an issue when someone breaks a rule to actually helping to break a rule :P
Arise, ye farmers of all nations
Arise, opressed of Tyria!
] before she committed to a purchase, and now that she has an account she wants to take her character with her. So, can this be done?