The Bhadaka planet for Libra ascendant is 11th Lord which is Sun. Also not to forget that there is lot of difference of opinion when it comes to Bhadaka concept. Many modern thinkers ignore it totally, while those who do suggest it, feel it is primarily for health purposes and nothing else. That is why I say that you test Blue Sapphire before you wear it. If it suits you then it will give you good results.