She may be scared, or just not really aware of how nice it can be to cuddle up!
With your original rat being so old, I would recommend you look for a pair of kittens asap, and then introduce them to your current two. That way Effie won't be left on her own, which is the last thing you'd want given that she's only just learning about companions.
When you find them, or sooner if that's going to take a while, I would suggest you use the carrier method to help Effie bond properly - details are here
. Go slowly, and keep them in the smallest space until you see Effie voluntarily cuddling up with the others, before moving up to the next size cage and do the same again.