Expect grief to look like quiet, not drama
A guinea pig whose cage mate has died may not do anything obviously dramatic. More often she sits in one hide for long periods, stops wheeking at the vegetable bag, picks at hay she would normally demolish, and startles more easily now that the companion who shared lookout duty is gone. Guinea pigs take confidence from each other, so the loss removes both company and a sense of safety at once.
Keep her world predictable while she adjusts. Feed at the usual times, clean the cage on the usual days, and keep the surviving pig in her familiar enclosure rather than moving her to a new space that strips away familiar smells as well. If the cage mate died at home, many owners find the survivor settles better when routines return calmly and quickly to normal, with extra human presence filling the gaps the other pig used to fill.
Watch appetite and weight as your early warning system
The real risk after bereavement is a quiet slide in eating. A guinea pig's gut needs a near-constant flow of hay and fibre, and a miserable pig who eats half her usual amount for several days can lose condition fast, particularly if she is herself elderly. Weigh her every few days on kitchen scales at the same time of day, and note hay, pellet, and vegetable intake honestly rather than assuming a topped-up rack means food eaten.
Offer favourite foods by hand, sit with her during floor time, and add gentle interest to the cage: a new cardboard hide, a hay-stuffed tube, a rearranged tunnel. The aim is not to distract her out of grief in a day, but to keep eating and moving woven through the day while she is low. If she refuses food entirely, produces far fewer droppings, or loses noticeable weight, contact a veterinarian without waiting to see whether mood explains it, because in guinea pigs appetite loss quickly becomes a medical problem in its own right.
Decide about a new companion at her pace, not yours
Most guinea pigs do better long-term with company of their own kind, and human attention, however loving, does not replace another pig's constant presence. That said, an introduction made in the first raw days, or with an unsuitable partner, can add fighting and stress to grief. Talk to a rescue about a calm companion matched to her age and temperament, and ask about their bonding process and what happens if the pairing fails, before bringing any new pig home.
If she is very elderly or unwell herself, the kindest answer may be a companion-free final chapter with intensive human company rather than the upheaval of bonding. There is no single correct choice; her age, health, and how she responds over the first couple of weeks are the evidence to decide from. Watch whether she gradually resumes calling for food, exploring, and resting stretched out in the open, which are signs she is adapting whichever path you choose.
Keep a clear record of the weeks after the loss
Note the date of the cage mate's death alongside her weights, appetite notes, and any vet visits that follow, because a slow change spread over weeks is hard to judge from memory and easy to miss. That record also helps a veterinarian decide whether low mood, dental trouble, or another illness is driving a drop in eating.
For keeping that thread together, KinsLe's Pet Passport holds this guinea pig's records in one portable packet, so her weight notes after the bereavement, her vet history and her usual routine are ready to show at any appointment without hunting through separate notes.