FYI, there is a secret ending centered around Giselle.

[Diana Nemorensis]

I've played this game a dozen times at this point. It's only with my latest playthrough where I uncovered, by accident, the exact set of steps you need to take to form an alliance with Giselle.

You'll know you're on the right track if you get an extra scene with her while investigating Scarper and the Pine Island Retreat with Nin. Mild spoilers below:

I had first investigated Neo Albion with Elton and uncovered valuable information I was then able to use on Giselle once I was investigating with Nin.
You can always temporarily partner up with Giselle during this segment so long as you pass an INT+Academics check, but it's very easy to miss the extra information with Elton beforehand or to do the sequences the other way around, which will lock you out of the next sequences.

You'll know you're on the right track after this if during the second Hog Throne chapter, Giselle comes to YOU asking, quite fervently, for an alliance. You won't need to pass a skill check with her if this is the case. You can accept or turn her down on the spot. If you accept, she will now ally with you against the Cult of Fenris and she will help you during the whole prep stage against Kemod/The Knight of the Stolen Moon.

You'll still have to fight her after Kemod because she's harassing whichever companion you left behind, but it plays out a little differently.

Finally, if you've been following along with this and general have been pro-Giselle the entire game, when you meet her again in the final chapter she'll greet you with "You look well' and you once again have the chance to ally without needing to pass a skill check. Accept, and Giselle will help you with the entire lead up to, and during, the final boss. Just like Daphne and Black Tarn, using Giselle guarantees you a success and adds interesting flavour.

Even if you never teamed up with Giselle before, I think it is still possible, if extremely difficult, to get her to switch sides and help you against Eater-of-Names at the very end if you pass a CHA+Persuasion check, but even with 7 dots I couldn't pass this.

Now, the end game spoilers:

Giselle will still lose her arm regardless, but in the epilogue you'll get a new option to go after her, confirming that she survived.

What happens after that... I'll let you find out.

[Abaddon]

Haha she's too horrible to die

[Stranger]

In my only playthrough I didn't have an alliance with her, but she and I were partners for most of the final act.

SPOILERS

During the mission where you are investigating the moths, you can meet up with her at the Hospice/Retirement Home and you will find out she has sentimental attachments to one of the patients who is killed by their son Drax. She will assist you for the rest of that mission if you share Drax's involvement in his father's murder. At the end, after you killed Eater of Names for the final time, and stopped the Drill, she will trap Answering Tiger in the dimensional maze to save you when he attacks your pack. However, the Answering Tiger manages to corrupt her through the point of physical contact where she drops the artifact she's made releasing Answering Tiger. Melodie saves her life by cutting off her arm and then everyone kills Answering Tiger and, well, you get every possible happy ending. The Garou killed by Answering Tiger who had lingering figments, like Katherine and Linnis, continue to exist and aide Garou all over the world, you share information on how to overcome the Wyrm's new tactics, reversing much of the recent gains, and Garou begin flourishing across the entire face of the earth and Gaia begins revitalizing the planet from the cairns you revitalized with the aide of the spirits you redeemed and reawakened with new purpose, including the lightning cat.

[5H4D0WDU57]

After multiple failed attempts, I looked into the game code. You need Kali's mark to track her, definitely don't need to buddy with her.