Marilyn had a limited race schedule in 2010, but returned to a degree of form when taking bronze at the UK championships. Subsequently, Okoro was selected to challenge for a medal in the 800 m alongside Jenny Meadows and Jemma Simpson at the 2010 European Championships in Barcelona. She finished 4th in her semi-final, therefore did not progress to the final. Okoro recovered from that disappointment to run the second leg in the 4 × 400 bronze medal winning quartet alongside Nicola Sanders, Lee McConnell and Perri Shakes-Drayton, clocking 52.0 seconds for her leg. She also ran in the heat running 51.8 seconds. Vicki Barr replaced Shakes-Drayton in the heats.