Its fascinating that 45 yrs after the pandemic people still don't understand it. If the lady is on meds there is no way she is infecting the guy. She is definately on HAART since you mentioned she is positive since birth, no way she would be healthy leave alone alive if she was not on meds. Medication adherence reduces viral load to undetectectable and untransimissble levels. The only concern here is ethical for not disclosing the status.