Well, I'm hoping that she chewed it, as it may be too late to make her vomit it up now. I suppose you can still try it if you want, I just don't know how successful it would be.
Also, do you know what kind of peanut it was? They do make ones that will just dissolve in water now. If that's the case, then you probably don't have to worry too much.
If she swallowed it whole and becomes obstructed, she would most likely start vomiting in the next few days. She may also show abdominal pain, and lose interest in eating. It would be very uncommon for them to continue to eat if they are obstructed. If she is showing these signs, I would take her to a veterinarian, as surgery may be necessary at that point to take the peanut out.
I would watch her poop daily for the next week or two to see if it comes out.
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