If she is a legitimate owner, you can't force her to sell her interest in the house. You can communicate indirectly with her, perhaps through a lawyer, and see if she is willing to sign something authorizing you to sell. Unless she is mentally incompetent, you will likely have a very difficult time of proceeding with a legal challenge. At minimum she should be paying you rent, if she is the sole occupant, and if she is unwilling to let you live in the house or pay you rent as co-owners, you could possibly proceed with a suit along those lines.
This is a good example of why it's not ideal to co-own a home with someone you aren't legally married to, including a relative or someone you are dating, because there is no (relatively) simple process similar to divorce which determines the allocation of property in the case of a serious dispute. If living together, it may be preferable to have one party own the home and rent it to another. If inherited, it may be preferable for one party to buy out the others and rent it back to them or arrange for a portion of any money made through the sale or rental of the home.
Best of luck - I hope you are able to reach an agreeable outcome.