Lifelong cage-mate is gone. Now what?

one of my two lovely rescue girls passed away a week ago from surgery complications for dental damage from her past neglect. I'm worried about her sister. They're both 5 and have always been together. Would a new cage-mate make her happiest? And if so how long should I wait? There's an 8 year old girl up for adoption nearby (also a 3 and 5 year old but my girl has a history of abuse). I know if introductions don't take I need to house them separately and I'm prepared for that. Otherwise...

Lifelong cage-mate is gone. Now what?