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Miss Understanding Fixes Her Life mostly fits. It fails on the last point but shadow stalker was already out of the wards before the fic started for AU backstory reasons. Also the ward she is dating is part of why she is recruited but not the only reason.

https://forums.spacebattles.com/threads/my-fake-girlfriend-is-a-vigilante-au-alt-power-tinker-taylor.849952/
My fake girlfriend is a vigilante has her fake dating then real dating Shadow Stalker, Taylor gets recruited into the Wards just not quite by Sophia.

https://forums.spacebattles.com/threads/no-greater-love-worm-au.951384/
No greater love has an alternate Taylor dating Sophia and dying to Leviathan while canon Undersiders Taylor gets transported to that universe and sort of recruited by Sophia.

Those are the only two I can think of where both romance and Wards recruitment are involved, just not exactly your request (also both are shadowbug).

There's a fic where Taylor can control mice and/or rats, I can't remember, and is in a throuple with Vicky and Dean. I don't remember if she was independent or if Dean recruited her into the Wards though, or the name of the fic.

Edit, 'cause I forgot some that don't completely fill your request but meet a few parts:
https://archiveofourown.org/works/30186441/chapters/74376411 Just A Phase has her be a (uncooperative) Ward in Boston, no romance, Shadow Stalker is a Ward in Brockton, no Undersiders.

https://archiveofourown.org/works/55520581/chapters/140900065 has her be a Ward in Boston but run away to Brockton, no romance, don't remember if Shadow Stalker is involved, no Undersiders (I think).

https://forums.spacebattles.com/threads/implacable-worm.840956/ Implacable has her be a very uncooperative Ward, no romance, Shadow Stalker is still a Ward, Undersiders are just mentioned I think.

https://www.fanfiction.net/s/13531154/1/Lord-Doom-by-RustPony LORD DOOM has her join the Wards, no romance, Shadow Stalker is still a Ward, Undersiders appear for a chapter or two but otherwise don't matter.

https://forums.spacebattles.com/threads/the-techno-queen-worm-au-humour-with-extra-ham-cheese.300011/ The Techno Queen (krakathoom) has her be a villain, there's a romance with Clockblocker, Shadow Stalker is a Ward, the Undersiders are her minions.

https://forums.spacebattles.com/threads/a-ghost-of-a-chance-worm-v1-cyoa-alt-taylor.766498/ A Ghost of a Chance has Taylor join the Wards near the end, no romance, I don't remember if Sophia is in the Wards still, the Undersiders have a role in the beginning but it's antagonistic.

https://archiveofourown.org/works/24628690/chapters/59501623 She dates a ward from another state sveta a case 53

!remind me 1 day

I've got one that may fit the bill: A Brush With Darkness

Superpowers were a poor consolation for a year of hell, but now at least Taylor Hebert can help people. On her first night out she's lucky enough to encounter Shadow Stalker. The Ward takes her under her wing and shows Taylor what it really means to be a hero. But what does their relationship look like from the outside looking in?

I wrote That Others May Tinker, in which Taylor is dating Dennis. She isn't in the wards though.