She went from being housed with her siblings to being housed with Tank. They were always cuddled up together. Should I place something in the enclosure for her?
I think (as in personal opinion), that she will adjust to being alone just fine. Maybe do a little spoiling giving her what ever she likes to eat the most. Maybe change up her enclosure (as in rearrange it) so it's not the exact same place where she expects Tank to be. Give her some time and see if she seems to act like something is missing in her little world. By acting I mean does she seem less active or eating less. Normally tortoises seem to not miss when a tank mate leaves.
I also think Gypsy will be fine, not lonely.
I have a group of leopards and I notice they all seem "happier" when housed alone. With my different chambers and pens I'm able to rotate things around to give them some occasional alone time.
lichjen, two seems to be a not good number for tortoise keeping. The bullying seems to be hard on one or the other. It is not even obvious really, it's almost sublime. Keep Gypsy as an only for now. Like the book The Little Prince and his one and only special little rose. I have leopards, which is different species, but I am rather convinced that it is either one, or three ... never two. Just based on what I have read here and in other places. Hope you are healing! : )