It seems I always get a bit nostalgic for Downton this time of year (Jan. is when the series aired in my area) and I end up rewatching the show, well, series 1-3 at least. Anyhow, the garden party proposal that didn't happen always breaks my heart and although others, including myself,(After The Party) have dealt with it before, if you're interested, here's another one shot dealing with how Edith might have reacted to Anthony's walking away that day.
You'll recognize the material borrowed from canon.
Edith simply stared at Anthony's back as he retreated across the lawn. He...he had said, well, hinted, the last time he'd taken her for a spin in the Rolls, that he intended to propose at the garden party. It was a day the young lady would never forget. Mr. Bromidge and Carson were discussing the installation of the telephones at Downton when the tall blonde had unexpectedly arrived and inquired as to whether Lady Edith was in. The older gentleman had been so happy to see her, such a joyful expression crossing his handsome face, when, in her eagerness to see him, the strawberry blonde had, in the most unladylike way, hurried into the hall to announce her presence.
While on that drive, he'd pulled over, taken her hand in his, and told her that he had a question for her and that he'd ask it at the garden party and that he hoped she'd say yes. Today though, the normally mild mannered baronet appeared to be angry with her. No, that wasn't quite right she thought, the look he'd given her as he turned to leave seemed more as though he were hurt or disappointed. Perhaps both. What could possibly have happened since that glorious afternoon just days ago to cause such a drastic change in his demeanor towards her.
Glancing defeatedly through the crowd, she saw Mary's evil smile of triumph as the dark haired beauty raised her glass mockingly in Edith's direction. The strawberry blonde felt a sinking sensation in the pit of her stomach as she realized her older sister was responsible for Anthony's sudden departure. Gripping the back of a chair to steady herself, the young woman struggled to contain the painful sobs that threatened to erupt from the depths of her heart. A battle raged within her broken soul, should she go after Anthony or would it be best to wait a day or two before speaking to him? Oh god, her future, her happiness was at stake and Edith had no idea what to do. The young woman made a decision rather quickly though, once Lord Grantham announced the country was at war with Germany. Mere moments later, Edith Crawley was headed to Locksley.
Edith knew the baronet had served in the Second Boer War and her Anthony, her noble, gallant, Anthony, bound by his sense of duty might once again offer his services to his country. Because, in his mind, it would be the honorable thing to do, she thought, as she brought the car to a stop outside his ancestral home.
Edith didn't bother with formalities, she simply entered the manor and despite Oakley's protests, strode nervously towards the room where she'd most likely find him, his library.
The tall blonde looked up, "Why are you here" he frowned, continuing to sift through the papers on his desk, setting some aside while stuffing others into a leather case.
"Are you going somewhere" Edith asked anxiously.
Anthony simply nodded in reply.
"Where? I was hoping we could talk."
"Edith, I haven't time for this. I'm sure Lord Grantham has received the news as well" the baronet waved a telegram in the air. "I'm leaving first thing in the morning for Whitehall to offer my services."
"What? No" Edith cried, crossing the room to stand beside him. "No! You can't do this! Please Anthony, please" she begged, "you can't go to war! If... if something were to happen to you...I'd... I'd be...devastated " the young woman sobbed. "Because...I..." her voice broke, "I love you!"