Evie Gane has penned a dual-signing agreement with Championship side Watford.
The defender will remain a Pompey player, but will be available to train and play for both teams.
Blues boss Jay Sadler said: “I’m really pleased for Evie. It was only a matter of time before she attracted interest from higher.
“Her individual performances have been very good and highly consistent.
“She’ll continue to train and play with us for the remainder of the season, while also gaining exposure at Championship level.
“All of which creates a fantastic opportunity for Evie to continue her development in the game.”