If the scales are popping up then it looks to be dropsy. Dropsy can be caused by numerous things and only sometimes can be treated. Theres not too much known on why dropsy happens. The fish should be isolated and search for dropsy meds to pick which one to treat with.
Waterchanges should take place until there is no ammonia or nitrites.
If it comes down to it, watch her closely and if she is suffering a lot you may want to consider ending her suffering.