what do i do now?

cw death

i rescued 2 chinchillas a few weeks ago and one was doing poorly and she did go to a vet but had fits last night and passed away at the emergency vets. now i don't know what to do about her sister. already she's been lonely and sad just from a few hours of separation. they've had a horrible life of neglect and pain and have never been apart. i feel like i've failed them. what can i do to help her? she's 5. will she be able to adjust? how can i help her and what options do i have...

what do i do now?