Definitely try the water bottle; some people also have luck with shaking pennies in a can. What you need, though, is a consistent signal to train the cat. Anytime she jumps on the table, clap your hands loudly and say "Down!" in a sharp tone -- if you have to move towards her and get her down, that's fine (or clap hands, say "Down!", and then spray her with water). Over time, though, she'll understand that if you clap your hands and say "Down!", that she's going to get pushed down or squirted, and she'll start to do it on her own. But it takes time -- cats are a lot slower to train than dogs.
About the weight gain -- are you free feeding her? If so, I would stop doing that, and just feed her a specific allotted amount at certain times. You do NOT want to have a severely overweight cat (trust me, I speak from experience), as once they put on the weight, it takes years to get it off. Also, are you feeding wet or dry? Wet food is generally better, and helps to keep the weight down, because it's almost all protein, whereas dry food is almost always mostly carbs (corn filler, etc). Wet food is generally healthier, too, as it's closer to what a cat would actually eat in the wild -- back in the day, vets used to say to feed dry food because it helps keep the tartar off the cat's teeth, but that's been discarded lately as not being true (there is a very slight difference in tartar, but the pros of feeding wet over dry far outweigh that marginal pro). If a vet is telling you to feed dry for that reason, I would question their knowledge of the latest research.