If orf is about on your farm, then your ewes will have immunity to it, so unless your Herdy girl is under the weather, she shouldn't be affected.
However, if this lamb has brought orf to your farm and you didn't previously have it, then all your sheep could be susceptible.
Most healthy sheep will shake it off anyway - a few pustules, a few cracks and bleeds, it heals, all over.
Any that do get a worse dose of it will mostly still heal up and get better, but do watch out for any secondary infections.
Where there are suckling lambs then there are cracks in teats to allow the infection into the ewe's udder - and thence to the lambs. So be alert for orf on suckling lambs and check the mother's udder. If she's under the weather at all, including if she's struggling to feed her lamb(s), then she's at risk of the orf leading to mastitis. But if you are vigilant and treat any secondary infection immediately, all should recover.