Hi!
Older guinea pigs often prefer to have their own territory, but they still rely on the interaction and stimulation with other piggies through the bars. Rather than living together bonding, I would consider piggy neighbours she has full body visibility with so she can use all senses for communication - sound, body language and scent with being able to touch noses as well. this will prevent her from becoming depressed but give her her own space.
A C&C grid cages with just lino as flooring and no correx sides would be ideal for an older guinea pig in order to enable full communication.
Here is a picture of my own set-up. I have over time had several tricky old (and not so old) ladies. Some have eventually agreed to move in with another diva, others have preferred to stay single, but they all have relied on interaction through the bars.
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I am keeping my fingers very firmly crossed for poor Gingernut!