The lifting table pg: 321
Keep in mind that each level represents
what a character can lift by expending all
of his effort; he isn’t really going to be able to
move much more than a zone carrying something
that’s equal to his base Might. A character
can carry something two levels below his Might
for a short distance (allowing him to make a
sprint roll restricted by Might, with the item’s
difficulty as a border value). He can carry something
four levels below his Might with no real
penalty or can toss it a distance of one zone.
Something six levels below his Might could be
used as a thrown weapon
I've added Bolded and italics:
As you can see, this character can only throw something the size of a child. So, somewhere between 40 and 80 lbs. Not motorcycles. She could throw something the size of an adult 1 zone...but that wouldn't be an attack against anyone. I might let it be an attack against a
person they are throwing 1 zone. To attack with a motorcycle in melee she'd need at least Supernatural Str.
I wouldn't let the +3 to lifting add to the attack. I say she uses her might (+5) to attack (as a stunt)...basically, she uses Might instead of weapons for the
purposes of attacking with objects. This lets her attack in melee with, say, a street sign (weapon 3, I'd say) or throw said street sign like a javelin using her Might. She's limited to what she can lift (as I quoted above). The weapon value of stuff she throws would be up to GM and she'd add her Inhuman Strength value to those attacks.
So to summarize: Assuming they have a stunt to replace Weapons with Might, an item 6 levels lower than her carrying capacity can be used as a thrown weapon while an object 4 levels lower than their carrying capacity can be used as a melee weapon. The total skill of the attack is the Might skill. (not Might + Lifting bonus)
I don't think this is much more powerful then, say, a character with a Weapons skill of +5, a str. Power + stunts weilding a claymore or having the "claws" power.
EDIT: my math is bad. @+8 lifting, she could throw a "most furniture or heavy set adults" (200-250lbs - they mention heavy-set adults, not morbidly obese adults) and use couches and similar objects as melee weapons (300-400lbs, I'd say). It jumps from +3 to +7 and a motor-cycle is around 300-1000lbs depending on the type...
Edit 2:
Weapon damage.
I would also limit how high weapon damage goes. Even throwing a car (assuming you had a lifting of +14) I'd limit it to weapon 4 or 5. Instead I'd let larger objects do spray attacks and, in very,
very rare situations**, a zone attack to represent the size of the object taking more space and hitting more people.
**By invoking an appropriate character or scene aspect...