10
Joanna Whitton, 48, of Ty Gwalia, Penarth was stopped by police on Junction 30 in Cardiff on April 7.
She pleaded guilty to having 85 microgrammes of alcohol in 100 millilitres of breath.
The legal limit is 35 microgrammes of alcohol in 100 millilitres of breath.
Whitton also admitted driving without due care and attention.
Whitton was disqualified from driving for 20 months and ordered to pay £365 in a fine, costs and a surcharge.
