Polearms and Shortbows
If you ever ask yourself what the best medieval weapons are for someone, 7/10 times it’s a pole arm of some kind.
Your anime tier seven year old still has short arms, so they need to compensate for their lack of reach. Therefore they need a long weapon. A halberd, bec de corbin, glaive, Dane Axe or warhammer allows for good reach, the ability to stab, and the ability to cut or crush. You always want to be able to do at least two of these three things, so that way you have options in combat. Blunt trauma is also good against armored opponents. Stabs can also make it through chain mail if enough force is applied.
A mongol or Turkic style composite bow would also be a very good choice of weapon for someone small with super strength, as they have admirable draw weights but a relatively short draw distance and height, which would allow someone with short arms and super strength to use it with ease. Bows are good because you can kill from a distance.
In short, give them a halberd and a composite bow.
EDIT: Actually, you should probably just give her the bow, there’s a lot of issues wielding any decent sized pole arms with someone so small.