Assuming your parents are deceased, if not everything goes to them, you and your sister inherit in equal shares. As the Letters of Administration have been issued in both names when these are presented to the Banks, Ins Co's etc they should issue all the payments in your joint names which she won't be able to pay into an account in her sole name. The Solicitors dealing with the sale of the house will also require both signatures on all documents. It should be difficult for her to get round, point all this out and tell her you will get a Solicitor if she does not start complying immediately.