1993 capped off Timothy Zahn's Thrawn Trilogy with The Last Command. Grand Admiral Thrawn has acquired most of the Katana Fleet Dreadnaughts and thanks to the Imperial storehouse he found in Heir to the Empire, has an army of rapidly-grown clone soldiers to bolster his forces. While he prepares for a grand offensive against the New Republic.
Luke Skywalker investigates the nature of the clones and encounters the now-allied Noghri. Leia gives birth to twins: Jaina and Jacen Solo. Talon Karrde tries to form a Smuggler's Alliance for mutual protection among freelancers from the Empire. Niles Ferrier bites off more than he can chew. Joruus C'Baoth finally goes off the deep end. Disgraced senator Borsk Fey'lya finally does something productive. Garm Bel Iblis and Mon Mothma put their grudge aside. Leia, her assistant Winter and Talon Karrde's ace slicer (hacker) Ghent uncover the information leak on Coruscant. Mara Jade takes several hard looks at where her life has gone and where she wants it to go.
There's much that could be said about the book, but that would ruin the experience of reading it, and read it you should. Thrawn's cleverness is on display with some of his most creative tricks, and Bel Iblish shows just how capable he is of keeping up with the Grand Admiral.
Not to sound like a broken record, but the action, the character interactions, the traveling, the big crazy ideas that populate the galaxy, EVERYTHING oozes Star Wars in the best possible ways and the final showdown with C'Baoth is supremely satisfying in a variety of ways.
So, since that was a fairly short review of the book itself (by necessity, since otherwise it would involve spoilers) let's talk about strong female characters in the Expanded Universe.
There were a hell of a lot of them.
Zahn's trilogy in particular sets a very high bar since essentially every female he introduces is a supremely competent badass in multiple ways. Mara Jade is the biggest example: a wanderer coasting along the fringe after her life as the Emperor's Hand (A spy and assassin trained in the Force) abruptly ended, she gets drawn back into conflict and the echoing last command of Emperor Palpatine ordering her to KILL LUKE SKYWALKER. Through it all she undergoes significant character development, reconnecting with the Force and rethinking her hatred of Skywalker. She's her own woman, with her own goals and motivations, but makes an exceptionally good adventuring partner with Luke as the more cynical of the two. Mara was so popular among fans that Lucafilm eventually actually went and hired a real model to dress as the character and official art would use her face/appearance as reference material. As far as heroes that the Expanded Universe added to the Star Wars franchise, the woman named Mara Jade sits uncontested at the top.
Leia Organa Solo's aide, best friend, and long time rebel intelligence agent Winter is another strong addition. A fellow Alderaanian with stark white hair and a perfect memory, she appears here as a side character helping Leia out with intelligence gathering and data sorting, but the character would end up appearing quite a lot in other materials and grow into her own (especially in the X-Wing series).
Even Garm Bel Iblis' two most trusted subordinates are women: Sena and Irenez (who feature most prominently in Dark Force Rising). Then there's Shada D'ukal, a very small role who's introduced as a space pirate's arm candy, but ends up being a deadly hired bodyguard in a firefight. Let's not forget Leia herself, negotiating the defection of a race hell-bent on honoring their debt to the Empire while she's heavily pregnant with twins.
While they're all some flavor of “badass warrior lady” each one's different and has different areas of skill and different flaws. Its great stuff, and the vast number of clickbait thinkpieces out there saying that “Star Wars FINALLY has a Strong Female Character in a lead role!” are, frankly, insulting to anyone who's ever dipped even a toe into Star Wars past the movies. These are good characters. Strong characters. Strong female characters, and they're being completely erased by a new continuity and a “Narrative” that can only assert itself by dumping what came before into the Memory Hole.
But yeah, read the Thrawn Trilogy. Its good Star Wars.