Just because you have acres doesn't seem to be a reason to not have her spayed - the only reason for that is if you want her to have more kittens but that's a different thread, similarly for the tom that's run off. If she were mine and making all this noise unusually I would be back to the vet for a further opinion (although my first thought would be she's in season and calling but I assume the vet ruled that out?). Did they say why they've given her antibiotics, did she have a temperature? There must have been a reason.