The paper investigates a Hungarian-English bilingual child's Sarah's second language acquisition (SLA) with a special focus on how she integrated English (L2) into her speech to convey the intended meaning and negotiate the multiple identities she developed in her bilingualism in various social contexts. An ethnographic single-case study research seemed to be a relevant method of giving an exploratory, interpretive, and in-depth description of my single participant's language development (Creswell & Creswell, 2018, Duff, 2007). The applied qualitative data collection comprised the participant's everyday interactions, semistructured retrospective interviews, and her own spontaneous reflections. The findings indicate that Sarah used L2 as a complementary set of linguistic forms to differentiate meaning and as a social site for negotiating and gauging her own and her interlocutor's conduct and language use. Use of L2 expanded her linguistic repertoire, conveyed communicative intentions, and shed light on her transitory bilingual roles. The various feedback she received from her social environment shaped her self-concept and called for discussing and revisiting her own language competence. What she thought about peer feedback exerted a powerful impact on her self-image. The study might provide incentive for teaching English to young learners in home settings and might underpin the relevance of investigating single-case scenarios.