Thea is one of Britain's most exciting young multi-event athletes, combining elite ability in the heptathlon with proven credentials in the long jump, high jump and 100m hurdles. Her breakthrough came in 2023 when she recorded the fourth-highest heptathlon score ever achieved by a British U17 athlete, while also winning silver medals in the high jump and 100m hurdles at the Commonwealth Youth Games. She continued her rapid development in 2024, setting three personal bests across five events at the England Indoor Championships before going on to establish herself on the international junior stage.

In 2025, Thea won silver in the long jump at the European U20 Championships in Tampere, jumping a personal best of 6.44m. She also won her first British indoor combined-events title in 2026, taking gold in the pentathlon, before winning the England U20 heptathlon title outdoors. Thea was selected to represent Great Britain & Northern Ireland at the 2026 World Athletics U20 Championships in Eugene in the heptathlon, long jump and 100m hurdles. She opened the heptathlon with a championship-best 13.23 in the 100m hurdles and went on to record a 6.39m season's best in the long jump. Despite a hamstring injury, Thea battled through to place an incredible 4th on the worlds stage.