Code:
<img src="https://www.femaleagentgame.com/wp-content/uploads/media/avatar/23_abs-sixPack-fair.png" style="position: absolute; left: 0; top: 35px">
This HTML element is all you need to make our heroine have abs at any point in the game, simply hit f12, click on the avatar with the picker and add the line as an element and the abs overlay is fitted in place.
As to why this isn't something you can choose to have from the beggining, it's a mystery.
Sadly the element gets overwritten every single time you advance the game or if you customize your character from the game itself. It would be possible (and extremely simple) for the dev to simply add an abs on/off toggle.