Ellie's experience of not being taught sign language until she was 14 years old may impact her communication skills and social interactions. Out of the given options, the most likely task that might be difficult for Ellie to master as an adult is:
trusting other people
This difficulty could stem from challenges in communication and building relationships, which are crucial for establishing trust. While she may face challenges in other areas, such as organizing events or creative tasks, the foundational aspect of trust in interpersonal relationships may be more significantly affected.