Introducing two chins- is this aggressive or normal??

Hi everyone,
I've owned chinchillas for a year and a half now. I originally adopted a pair, but I unfortunately had to have one put down due to malocclusion in June. About 2 months ago, I adopted a new chin from someone who had to rehome her. They are both females.
Rory, the chin I had originally, is 3 years old. Boo, the chin I adopted recently, is 4-5. They have been living next to each other in separate cages since I got Boo. I tried one introduction by opening both cages, but Rory went right for Boo and grabbed a chunk of her fur, trying to bite her. I immediately separated them and they have been just neighbors ever since.
Now, when I let Rory out for playtime, she'll run over to Boo's cage and try to bite her nose whenever she sniffs her. I want to introduce them in their play area, "neutral territory", but I'm nervous Rory will go right after Boo again. They're so fast, I don't want Boo to get hurt! Is Rory being normally territorial, or is she just plain aggressive?? Opinions and advice is appreciated. I would be ok with them being just neighbors,but it is a big pain to have two separate out of cage playtimes for them.