The bandages will only do the same job as a pair of brushing boots i.e. they will give protection to the legs whilst being ridden, from knocks and the like, rather than actually giving her support.  To build up her muscles you could try lungeing her in a pessoa type training aid (you can get one very similar to an actual pessoa on ebay for a fraction of the price of a real pessoa) and also by doing some conditioning ridden work.