Im having issues with my husband's ex-girlfriend!?

Firstly your sister in law needs to keep her nose out of your business. Secondly, what use would you be at a funeral, possibly causing an atmostphere because your hubby's ex would be jealous and deliberately making you feel uncomfortable, and thirdly, I don't see your step daughter would have gained any benefit from you being there - you are her step mum, and not her real mother where the bond of the family is - after all, it is her mum's father who passed away. Don't get paranoid over everything though - it will ruin your life. The sister in law has absolutely nothing to do with the whole situation.