Hey there! I used to have 4 piggies myself so I'm there. Haha I had to give them away in preparation for going away to college this fall and I ended up not going away! >.< Sad day.
Anyway, she will probably take very well to having a friend. The age difference probably won't be a big deal at all. When one of my first pair of piggies died I got a new pig that was 6 months and successfully introduced her to my then 4 year old, no issues. She'll probably get more active than she ever was before with a friend. Do you know all the "bad" intro signs to watch for and stuff? I can point you in the direction of some great piggy intro links if you'd like. =)
I also introduced a 6 month old male back into my 'herd' (a 5 year old by that point, a 1 year old and a 6 month old) after he had been separated at 4 weeks because he needed to be neutered and it went relatively smoothly. His mother was actually the biggest issue. She'd chase him around like crazy pulling out his hair and stuff but I just ignored it and they were fine a week later. The only reason they were fine though was that my cage was large enough for all 4. It was 16sq feet (not sure how that translates to meters, you'll want about half that so 8ft, for 2 piggies to be truly happy and comfortable) and they each had their own spots to hide and stuff.
That boy pig was the friendliest little piggy ever and even after going back in with the herd he was still just a friendly. He would sit there waiting for you to pick him up, even when all the others were running around freaked out.
I even wasn't home for a month, no one picked up dexter and when I came back he did little popcorns and ran up to my hands to be picked up. All because of how "imprinted" he was in his 5 months alone.
My oldest female on the other hand was super snuggly when she was by herself but with other pigs she couldn't get away fast enough. I think in her case it was more caused by her up bringing (petstore pig into a loud family, the family before mine, who would hold her for hours with no escape, etc).
I think your piggy be fine. Just make sure that your new pig has been separated from all males from 4 weeks old and you'll be good to go. You'll also want to do a one month quarantine with the new pig in a completely different room from Topaz just to make sure she's healthy.
And if it helps at all: piggies by themselves are like human little kids without any other little kids. They act fine and everything but once they get around others of their own kind they light up. They can both be happy on their own with only adults/humans for attention but in the presence of ones who really "get' who they are, they're so much healthier emotionally. Yknow?
Good luck! =) Feel free to pm me with any questions you have or funny stories, I love talking "piggy". =)