Thank you for your query. Im sorry you are put into such a quandry.
According to Centre for disease control any positive titre is considered positive in pregnancy. You would be best advised to see a doctor specialising in skin and DVD. Although the titre is low, the doctor will be able to decide from your previous reports if the original treatment was adequate as and whether she needs repeat treatment this time. The review titres are also important. If she didn't have them done last time its important to get treated this time. Since penicillin is safe in pregnancy and she is not allergic to the drug it should be OK.
with best wishes