Hello, I'm Dr. Deb. I see where the previous expert with whom you were discussing Boots' lameness issue has opted out of your question.
If you still need assistance, I'll be happy to try and help if I can.
If a cat has broken a bone, in most cases, the patient is going to be pretty painful/uncomfortable when you palpate the site of the fracture. This is generally true when the break is located below the hip. However, if there's a break at the top of the femur (which attaches at the pelvis), then it may be more difficult to identify that this is the problem without an x-ray. Boots should still react, though, if you press hard enough in this area.
Soft tissue injuries (pulled muscle or ligament, strain/sprain, etc.) are much more challenging to identify since it's often very difficult to localize an area of pain or discomfort. This is often a diagnosis by excluding every thing else which might cause a cat to become lame or not bear weight on a leg.
I've seen quite a number of cats with abscesses or bite wounds with lameness issues but usually you'll notice a swelling or scab or discomfort when the spot is touched or palpated. And, usually these cats are putting weight on their limb but are limping when they walk.
It's also possible that she's ruptured her anterior cruciate ligament (ACL). This is a problem more commonly seen in dogs but it can occur in cats as well.
If she has a luxating patella (which means her kneecap moves in and out) and she experienced some sort of trauma (such as jumping and landing wrong), then she might also avoid putting pressure on her leg.
As you can see, there are quite a few possible explanations for her behavior with this leg which an x-ray might detect if a thorough physical exam doesn't pinpoint the problem.
I would dearly love to recommend an over the counter treatment option for her but as Dr. Peter mentioned, this wouldn't be wise since so many of these products can be harmful to cats.
I wouldn't consider this to be an ER type of situation..not yet anyway especially since she's eating....but if she continues to only walk on three legs, then a vet visit may be prudent.
I hope this helps. Deb
PS: I have to step away from my computer for a bit to help a neighbor with health issues but I'll log back on later if you have additional questions or concerns. My apologies for the inconvenience.