I need your opinions please

I got a new admission about 3 weeks ago. the resident is the mother of a ex-coworker that I knew long time ago in a non-related nursing job. She is not my friend, but at the moment I met her in the unit she was so happy that I work there. I am fluent in a foreing language. Eventhough she speaks English very well, she prefer to talk with me in that language. Her mother does not speak English at all, so she is very happy that I speak her native language. I feel akward when she call to the unit to be updated how resident is doing and the nurse manager answer the phone and resident's daughter ask for me. I come to the nurse station and talk to her in that foreing language and only English speakers are around there. I feel very bad, I think is rude speak another language in front of only English speakers. Should I answer her in English when she talk to me in ------ language? I think that is rude too. Please give me your opinions or share your experiences with me. I make aware the nurse manager immediately about the conversation and document it.