a sister asked me for my opinion on concubines

I was at a dinner the other night and a sister (she's only newly baptised, maybe 2 years?) comes up to me (im 17M but I'm usually seen as one of the 'exemplary ones') and she asks me about the Watchtower on Sunday (I wasn't there and didn't read it so I had no clue what she was talking about). She asks me what I thought about concubines. My first response was 'what?'. She then went on to say that to her it seems unfair that Jehovah let Hannah be infertile in addition to the fact that her husband had another wife. And she said to me that she thought I had probably done research on it and wanted to know what the organisation said about it. Genuinely I just froze. I had no clue what to say. I just wanted to say how it's just one of the many contradictions of the Bible, and that god clearly is a changing person even though the scriptures say otherwise. The sister even brought this up, saying how she thought it was weird that god created the marriage arrangement between one man and one woman, but here he was condoning a marriage with two women and one man. I wanted to say that in the end there's only two answers: either you listen to the excuses of the organisation and just agree, or realise that it's a contradiction, and one of many.
but in the end, i just said 'I don't know'. I felt awful though. I wanted to tell her the truth. But I couldn't. I hope she realises it.