In my AU, Surge is the "definitive cyborg", which means that the same metal virus inside her body will continue to fix her cybernetic parts. The only way to stop this is to disable a very little part of her skeleton, which only Starline knew where it is placed. Still, in post LTMEA, when Surge gets better at trusting people, she still gets checked out by Tails, just to be safe.
Autumn and Kit are another story, which the first is a very rough prototype cyborg and will decay very soon and Kit has got his weakness spot, found in the core of his backpack, destroyed by Starline before the platypus would die. This caused Kit to be unable to fix himself and decay later in the story as well.

AU Surge has got one official transformation in LTMEA, which is the Overddrive version of herself.

(Some old pic about the transformation https://x.com/exSURGEt/status/1767304931239702656/photo/1 and https://x.com/exSURGEt/status/1741595089397530990/photo/1)

Pretty much Surge's whole body would be covered into white electricity to the point it feels like she's not tangible anymore. She gets unstable, impossible to control and its pure raw energy striking whoever gets in her way. It consumes her stamina a lot and it won't last much.
A little warning here, it may be graphic the aftermath: In my original idea of Overddrive Surge, her skin and flesh would burn away from her cybernetic endoskeleton, making her look like a very skinny android. It would take her half hour or one hour to regenerate herself back to herself.

Now I'm not sure if I'm keeping this gruesome idea for LTMEA. It is from an old draft and probably it is TOO MUCH EDGY, but I still wanted to tell this little trivia anyway. :P

Gabrielle, before turning into Surge, was learning the details and the powers of the green Chaos Emerald (Mazuri's emerald), but she never interacted with it because at the time she was just a simple L.Gaia nun and not the Guardian.
LTMEA Surge can just absorb ONE emerald power at the time (pretty much like she does with the chaos drives in the IDW comics) because she can't connect with the gems spiritually, like Sonic and others can do. Surge is too corrupted to open her heart to the emeralds. TBF I never tackle "Super Surge" in LTMEA AU, but I will speak by doing hypothesis: if Surge managed to grab all the 7 emeralds and tried to absorb their energy, then she would end up like Dark Sonic in "Sonic X", because she would collect the negative energy instead of the positive one.

Sonic and Gabrielle met in Spagonia before the events of Sonic Unleashed starts. Gabrielle (and Amos) were volunteering in Spagonia's L.Gaia temple and Sonic was passing by searching a place where to rest for the night after a long fight with Eggman. Gabrielle was really curious about knowing the Blue Blur because she would always read about him on the daily newspapers but she was kind of shy when it comes to speak with famous people. Luckily Jamala was with her at the time and pushed her to interact and help Sonic search for a place in the Temple where he could sleep for the night. From that day, they would start to get along when Sonic could visit her.
When the events of "Sonic Unleashed" started, both Sonic and Gabrielle then helped eachother out with the Dark Gaia's problem. Sonic would bring the humans and mobians who got affected by Dark Gaia and Gabrielle, alongside the other nuns and the Spagonian L.Gaia guardian, would exorcise them.
So, before Gabrielle turned into Surge, she knew Sonic for 2/3 years. She would develop a crush on Sonic, but because of her vows she would never confess it. Even Sonic was starting to really like this girl, but deep inside he's a shy dude too!