I once heard someone say (on being introduced to a friend's newborn boy called Freddie) "oh I like the name Freddie for a girl".
My reaction was which is similar to that for this OP.
Bertie is a boy's name. It's a nickname for Albert (or Bertram, or Wilbert maybe).
I really am not keen on boys' names turned into girls' names, sorry (eg Roberta, Nigella, Albertina, etc). Like them less than names that do for both boys and girls (and I have one of those).