Would a Medal of Valour burn a Malvora?

Your assessment is accurate for the source content; specifically, the author Jim Butcher's quote about the various White Court weaknesses confirms that courage and symbols of it would be their weakness.

“You’ve said that True Love (real True Love) only protects against WCVamps feeding on lust. What protects against the other WCVamps?”

It isn’t real complicated that way. The vamps who feed on fear get bad effects from real courage. Those who feed on despair choke on hope.

Furthermore, from Dresden Files RPG Volume one "Your Story" (p84)

Hey, Bob, is it only True Love that works here, or are there other...uh, Truths?

One could easily posit that True, and most importantly, selfless Hope or Courage would act as dire counters to despair and fear. But we have a decided lack of, shall we say, experimental data on that front.

For game purposes, it makes sense if other True emotions work, so I’m going to go with that.

However, the exact situation of the Medal of Valor might also affect its ability to repel a Malvora:

• Was the Medal justly earned, or was it given to someone for simply surviving?
• Is the Medal viewed by the recipient as a true representation of their courage?
• Is the Medal a current representation, or something that has been passed down for generations?
• Has the medal been held in reverence, or was it just unpacked from a dusty cardboard box?

If the Medal truly represents courage to the person who received or currently has it, it can repel a Malvora similarly to Love repelling a Wraith. Otherwise, it may not actually embody the courage you may think. The exact effect of this is not elucidated, but a few things are listed as consequences:

• "True [emotion] can burn them (leaving scars that don’t fade), and holy objects and displays of faith at least make them uncomfortable." (YS p84)
• The character's Inhuman Toughness and Inhuman Recovery would be compromised as True [Emotion] would be their Catch (YS p84 & p185)
  • This only officially applies to directly using the Medal against them, although most people would probably run it as a compel against the character's High Concept to remove themselves from its presence... or a Block against them doing anything while it's in contact with them.

Notably, Wraiths don't immediately flee from everyone wearing a ring so it can be assumed that, although the presence of it would make them uncomfortable, merely having the Medal wouldn't immediately scare off a Malvora. Even the intent to use it against them wouldn't necessarily mean they don't simply attempt to knock you out instead.