Bogo is right. It really depends if you are up to it or not. I know from experience, Labs are wonderful dogs. But, they take A LOT of work. If you have the time and patience for another dog, go ahead! Like I said, and I'm sure you know, Labs are great dogs. They are always happy and smiling. I know your dog would be open to having a friend. Right now would be a good time to get another one so they can sort of grow together. If you wait too long, the dog you have now could become too overprotective of her territory, and not want another one infringing.
Also, definetely get one around the same size as your Lab. They love to play, sometimes a little rough. So another Lab would probably be the perfect choice. Not to mention, you already know the breed's personality and characterisics. Hope this all helps!!