Marta is a classic tabby!!
Now I know what Dayle would look like if she ever got chubby. She won't. She's too finicky of an eater.
If Marta was on cat chow and not much canned with her other owner and is now on just a good quality canned she should drop some weight on her own. She should be eating between 250 to 300 calories a day. Normally one small can or there abouts. Some cans have the calorie content on them. Dry is nothing but pure carbs. Cats need protein, not carbs.
For toys you could get a laser light, a wand, anything interactive that you can drag behind you or wave in front of her to get her moving.
Love PK!!!