Allydia

‘She would’ve been with us.’ “She still is.”
 * - Lydia Martin

Allydia is the Femslash ship between Allison Argent and Lydia Martin from the Teen Wolf fandom.

Canon
Allison and Lydia first met in Season 1's Wolf Moon, and from the on, they were practically inseparable. Their friendship quickly grew to a close, almost sisterly relationship that was very similar to the brotherly relationship between Scott and Stiles. In the first season, Lydia helped Allison adapt to being in a new school and navigate her relationship with Scott McCall. After Lydia was attacked by Peter Hale in Formality, Allison was so distraught and concerned about Lydia's injuries and possible transformation into a Werewolf that she was more easily manipulated by her aunt Kate into attacking Scott and Derek Hale.

Throughout Season 2, Allison tried her best to keep Lydia safe by keeping her in the dark about the supernatural, which was ultimately detrimental to Lydia's well-being, since Peter's attack had triggered her latent Banshee abilities and she was struggling to understand what was happening to her. Though Allison tried to support Lydia as best as she could while keeping the secret of the world of Werewolves from her, Allison herself would eventually admit that Lydia's mental instability due to Peter's spiritual possession of her mind and her burgeoning Banshee powers were made worse by the fact that she, Scott, and Stiles had ignored her, making it the low point in the girls' relationship.

However, by the beginning of Season 3, Allison and Lydia's close friendship became stronger than ever, due in part to the fact that they were both single, as Allison and Scott had broken up at the end of the previous season, and Lydia and Jackson had also broken up after Jackson Whittemore moved to London. Allison dedicated herself to being a better friend to Lydia after the previous mistakes she had made, supporting Lydia as her Banshee powers continued to grow, and in turn, Lydia also helped support Allison after the loss of her mother. The two worked together to help figure out the plans of the Darach, the Alpha Pack, the Oni, and the Nogitsune in turn while they became more and more loyal to the McCall Pack.

*source Allison and Lydia Wiki*

Quotes
''“Did you find her? Is she okay? Is Lydia safe?”''
 * - Allison Argent

''“I don’t care. She’s my best friend and we need to find her before they do.”''
 * - Allison Argent

“…and you are my new best friend.”
 * - Lydia Martin

Fandom
Allison/Lydia tag on Fanfiction.net

Allison & Lydia tag on A03

Trivia

 * Both Lydia and Allison have made out with Scott McCall, though Lydia only did it once as a sort of power-play in Season 1 when she was still more of a mean-girl, while Allison was in a relationship with Scott for several months.
 * Their friendship is very similar to Scott and Stiles' friendship.
 * In an interesting twist, Lydia showed Derek Hale, Jordan Parrish, and Scott McCall a picture of her grandmother, Lorraine Martin and Lorraine's wife, Maddy, in Season 4's Perishable, in which Lorraine and Maddy closely resembled Lydia and Allison; Lorraine was a redhead with green eyes like her granddaughter Lydia, whereas Maddy was a pale girl with dark brunette hair like Allison. It is possible that this was intended to be parallel to Allison and Lydia's relationship.