My bee hives are in a corner of the sheep field, and the lambs run right in front of them (fenced off of course). Not seen any stings or similar on the ewes or lambs, also have horses coming past on other side of the fence, again, no one has ever mentioned any probems.
You don't have barbed wire or something the ewes could have been caught on?
However if she is fine, I would just keep an eye on it, if its a bee sting it will start to itch in a day or son, so she might start to scratch and rub the area.
PS. Also lots of queen wasps around at the moment, and I have been stung by a bumble bee earlier this month (from somewhere in her leg), and it was worse than a bee sting (as I get those all the time!)