Thanks for the additional information.
In a situation like this, I'd want to make sure that there weren't any underlying medical issues which might be causing Zoe to behave in an uncharacteristic manner. Typically, however, these dogs are going to show some other changes such as I asked you about.
But, some patients with conditions such as hypertension (which is usually secondary to other conditions such as kidney issues, diabetes or Cushing's Disease), for example, can behave in some odd and unusual ways so if Zoe hasn't had any blood work done recently, it might be something to consider to rule out these possibilities.
A thorough physical exam might also detect abnormalities such as arthritis which may be why Zoe is not sleeping on the bed.
I've seen some older dogs in the very early stages of Cognitive Dysfunction start to behave differently towards only certain members of the household but unless she's showing other signs such as confusion or loss of housebreaking, this condition may be difficult to prove.
Once/if these conditions are ruled out, then her reactions to your wife need to be taken within a context of more behavioral in nature which may be more problematic to explain or to change.
It's quite possible that Zoe is sensing or detecting something different about your wife (or by extension, your granddaughter) which is why she's keeping her distance. I'm a firm believer in a dog's ability to perceive problems about which we're unaware.
It's also possible that her nose (so to speak) has been put out because your wife "abandoned" her even though she's left her in the past. Older dogs don't tend to react the same way as younger ones do and often take longer to recover from what they might see as grievances.
I suspect your wife's feeling are somewhat hurt because of the way Zoe is behaving...at least mine would be if I were in her shoes. But, Zoe may just need more time to resume the relationship she had with your wife.
Your wife may already be doing some of the following but towards that end, I'd suggest that your wife try to spend as much one-on-one time with Zoe, doing things that they enjoyed doing in the past.
I'd also feed her special food during these times in an attempt to reestablish a more positive relationship with her.
I wouldn't necessarily try to force Zoe to behave differently but try to gently encourage her to interact more with your wife.
This is a tough situation, I'm certain, for your wife but, hopefully, Zoe just needs more time to work things out on her own. That by giving her the time to do so, she'll return to being the loving, "shadow" to your wife that she once was.
I hope this helps. Deb