Not a good idea.
First off, if she's a year old, the 30 gallon is probably already getting tight.
Secondly, the second turtle you get will most likely be smaller, if you get a hatchling, or bigger if you get a 4" turtle. Either way, the bigger one will bully, injure, or even kill the smaller one. Also, Buggie will view the new turtle as an intruder into her territory, so there will be tension right off the bat.
Two turtles means eventually a 200 gallon tank / pond, or two complete setups, which is a very big expense.
Finally, turtles are generally solitary creatures. They don't need a friend, and are perfectly happy being an "only child".
Both you and Buggie will be better off with just the two of you
