Without a diagnosis, there are multiple reasons for a single abortion, a knock in the field, a ewe with a temperature, an odd genetic deformity in the lamb.
If the ewe is well and eating with no temperature, there is NO reason to give antibiotics other than promoting antibiotic resistance which we do not want!
There is no reason to think that she'd be any more likely to abort the following year.
If she had an infectious cause, then other ewes are also likely to abort. Depending what it is(toxoplasmosis would be a prime example), the ewe can then be immune, and so would be less likely to abort the following year than one that has not aborted this year!
Like I said, get in touch with your vet as soon as possible if you have another abortion and testing asap can let you know if you have one of the infectious causes, and whether anything can be done now, or vaccination would be recommended for next year.