Later, at Leia's birthday party, she dreams of Green again and asks him what Donna Martin (Tory Spelling) was like between scenes and he replied, "What do you mean 'scenes?'

Source: https://comicbook.com/tv-shows/news/that-90s-show-70s-show-sequel-features-1990s-cameo-brian-austin-green-beverly-hills-90210/

So, that's pretty exhausting, and this gives her a sense of normalcy and excitement, as she's doing something else that doesn't involve the hospital," said Laura Kagumba, Leia's mother.

Source: https://abc7chicago.com/walk-the-runway-for-cancer-ovarian-lurie-childrens-hospital-fashion-show/14046433/

That said, the most simple reason for Leia's lack of appearance in episode 7 is the difficulties involving bringing Leia to the screen.

Source: https://screenrant.com/ahsoka-where-leia-is/