How old is she? Also how much weight has she lost? They tend to lose some weight when elderly because they lose muscle mass.
I wouldn't recommend feeding lots of mealworms for weight gain as they have far too much phosphorus and too little calcium and that can lead to other health issues. You can feed a couple per day but it's best to feed a wide variety of fat sources. In terms of insects, calci worms (black soldier fly larvae) are much better nutritionally. Waxworms are also high in fat (you'll probably have to buy these live from a pet shop). Mostly I recommend fatty seeds such as flax, hemp, sunflower, safflower, niger, plus nuts (especially almonds). You can also get flax/hemp/grape seed/evening primrose oil and drop a bit on her dry food every day. Also yoghurt, hard cheese, tofu, malt paste (sold for cats, dog and ferrets). There is also a supplement I use occasionally called Vetcal Pro Gel but I'd only really suggest that if she's continually losing weight (it won't hurt otherwise, it's just unnecessary).