This decision depends largely on your golden's temperament. Goldens are definitely pack animals and not solitary creatures - there is not an independent bone in their body and I believe a brother or sister is critical. With that said, there may be a right time to bring in a second. As others have mentioned, getting your current golden accustomed to everything and perhaps some basic training would be a good idea. They are very hard to train with a second dog.
If your golden shows no possessive tendencies, and is highly social, then bringing another one is a great idea - as long as she does not overbond with you in the meantime and become a jealous dog. Overbonding is a common issue with goldens.
Just make sure you have a handle on her before bringing in another and consider the age of the second dog - she is very close to maturity and growing out of a lot, as long as you get her instruction now on how to behave. A male older than her, who is calmer, could be a great trainer for her.
Good luck