I actually felt quite sorry for Lisa Nandy (yes I am a numpty) because I watched as the other two men and two women left her to PM's relentless questioning.
It felt like bullying almost because she was incapable of answering him, and he knew it. If she said yes, put the toughest ever male boxer in the ring with a woman she would look like a cruel, callous, ridiculous person, but if she said actually don't do that because he's male she would be letting down some 'side' which she was supporting.
In another venue Nandy said she was supporting a young girl going through the gender recognition act. Nandy said that young person would not hear anything from her that would give her any idea that she has anything other than her complete and utter compassion and support.
starting at 4:33
So I think her care for one person and her fear of being labelled 'transphobic' has left her in a very cold place where she has to pretend there isn't a really logical and simple reply for why males should not be competing against females.
I admire her for caring for one person but as a potential leader of a party she needs to see the bigger picture, and she simply does not, IMHO.
My only uncertainty here is whether she really does know why males should not be competing against females.