The bar is meant to be bought relatively early, maybe around mid game currently.I completed every girls story so far but for Ellen theres nothing in upgrades and no option to buy Jin
Edit: I also cant find a way to play through Juilet's story
After hitting "Upgrade" It brings you to this screen:
You don't buy Jin from Ellen, you buy Jin where you buy most items, on your computer.
Juliet doesn't have any events, check the patch notes.