Meg Edmonds is speaking publicly as part of an infection prevention campaign run by the Lullaby Trust, a charity that promotes infant health. She said her daughter Magnolia was born healthy after what she described as a straightforward water birth.
"I had a lovely birth with her, a water birth. She was nearly two weeks overdue like her big sister but everything was fine and she was born perfectly healthy," she said.
The virus is suspected to have been passed on by her mother. Only later, Ms Edmonds said, did she realise a sore visible on her lip at around the time of the birth may have been her first cold sore.
"Looking back at photos now I can see that I had a lesion or sore on my lip whilst I was giving birth which I thought nothing of at the time," she said. "I had never had a cold sore or anything before. I'd asked health professionals if they thought it was a cold sore, but I was reassured that it wasn't, it was nothing to worry about."
Ms Edmonds said she never kissed her daughter and washed her hands constantly because Magnolia had been born during winter. "But I never knew that if that passed to her it could kill her," she said. "I'd never ever seen anything about cold sores, HSV, neonatal herpes, nothing."
"The guilt is obviously unbearable, it's horrific, but I just try and remind myself that I didn't know and I did what I could have done with the knowledge that I did have," she added.
The Lullaby Trust's research has highlighted the pressure some parents feel when asking people not to kiss or touch their baby. Chief executive Jenny Ward said: "But protecting your baby from infection is never something you need to justify." The charity's THANKS advice, to think hands and no kisses, urges families to wash hands before touching a baby and not to kiss them if unwell.
For most adults a cold sore is a common but painful infection. In newborns, whose immune systems are not fully developed, HSV can cause life-threatening illness.