M.F Sent Twisted F. To Steal this Crimson-coil dagger
"Tonight was merely the endgame: Hiring T.F., tipping off Graves – all just to distract Gangplank. It had taken years to exact her revenge."
She wanted the dagger, So Miss Fortune hired T.F to steal that Crimson-coil dagger. She couldn't guess that T.F wouldn't make it and wouldn't instead deliver the job -- even with Graves being there. Maybe the dagger belonged to her parents and she wanted it back?
She wanted the dagger to reach Gangplank hands, And, does it mention anywhere that her parents were important? Or just random folk GP happened to kill in his ascension to power? If so, why was M.F so worried about being under the radar all those years -- "(...)waiting until she wasn’t even a memory to him, for him to drop his guard and get comfortable in the life he’d built." -- she was a child when he last saw her, and it doesn't say she, or her parents were any memorable, important foes. If he is this vicious killer, who again are the Jack and Jane he killed 15 years ago...
If she'd come up to him and say "AFTER ALL THESE YEARS!" -- wouldn't he just: "Errhh ... hi... you"
Unless they weren't just any family ;D or at least, what he wanted from them wasn't anything uninportant that wouldn't make him remember who he murdered to get it!
If her parents are some random folk, and so is she, why would've Gangplank have killed them? -- To steal a dagger that glows inside water! -- "The dagger is falling. Into the abyss. There it goes... Is it glowing?".
A possibility is that the dagger did belong to her parents and it has indeed some properties, or it is special somehow, and she maneuvered T.F and Graves there, both on different missions, not only to distract Gangplank, but for the whole thing to 'smell funny' for him. For him to think "Why this dagger?" -- before he met his end -- I assume at least, as it's usual, for the avenger to want his victim to see his face before the final blow.
TL;DR
- M.F hired T.F to steal a dagger that would hint to Gangplank that something bigger was going on.
- Put Graves into it for the job to take a wrong turn.
- It isn't stated anywhere that her parents are memorable for her to be so scared of entering Gangplank radar.
- The dagger is, however, hinted to be special -- a dagger that GP stole from her parents.
- GP by getting hold of the dagger would remember who and when he got it from by asking himself: "Who would want this?"
And then right after he got his eureka ----- BOOM.
