The 7th spot should go to a member of the X-Men and a female hero.
She also boosts minority representation, since she is Chinese-American.
As for her powers:
FIRST TREE: FIREWORKS
"Jubilee had the mutant power to generate bright bursts of multi-colored energy plasmoids from her fingertips. She referred to these globules as "fireworks". The globules obeyed her mental control, traveling where she directed them, arranging themselves in balls, streamers, and other shapes, and exploding when she wished. The strength of the energy varies in degrees of power and intensity, and could range from a multitude of colorful sparkles capable of temporarily blinding a person to a powerful detonation capable of smashing objects and destroying property, or a precision burst inside a human brain, simulating the effects of a massive stroke. Jubilee could absorb the fireworks back into her own body without harm."
There's at least one full tree for you, right there. Different types of fireworks -- balls, streamers, other shapes -- means AoE, DoTs and single-target options. "Temporary blinding" = stun powers. "Burst inside the brain" could be a cool single-target spirit-spender or even signature. "Absorb back into her body" = passive or heal ability. And "explode when she wished" would be a cool remote-detonation-type skill.
"While training in Generation X, Emma Frost described Jubilee as having the untapped potential to detonate matter at a sub-atomic level, which in theory is the equivalent of a fusion bomb."
Sounds like an awesome Ult, to me!
SECOND TREE: MELEE
Upon joining the post-Civil War New Warriors team, Jubilee gained highly advanced technology from Night Thrasher to replace her mutant abilities, giving her superhuman strength. While the upper limits of this power were not explored, the technology allowed Jubilee to lift the engine of a freight train over her head. Wondra's power suit and gauntlets also enhance her with limited invulnerability, as well as the ability to fly with hover discs.
Jubilee is a talented gymnast and in-line skater. While living on her own, she used her skills to evade capture while stealing to survive, first from the various shops in the mall and later in the X-Men's Australian base. She has also displayed above average hand-to-hand combat skills, having learned street-fighting techniques while in Los Angeles County Juvenile Hall, and being coached further by Wolverine.
Sounds like a cool melee/strength tree with physical damage, an in-line skating movement ability, and also flight using hover discs.
THIRD TREE: VAMPIRE
Jubilee has since gained the powers of a vampire from her transformation by the bite of Xarus, son of Dracula. Her powers include superhuman strength and speed, and the ability to turn into vapor. It is possible that she can heal much faster than a human.
As a vampire, Jubilee now possesses all of the weaknesses of a vampire. She must sustain herself on blood and avoid direct sunlight, garlic, silver, and religious symbols.
This tree would be totally optional and not the best spec, but she could potentially have a few powers similar to Blade, and some passive abilities that have some kind of trade-offs.