My fathers will?

1. You can very well claim rent from your sister for staying in the property, however you have to be careful that you do not develop any landlord -tenant relationship because it will be deemed that you recognise her stay in the property even as a tenant.

2. You were advised to issue a legal notice to her instructing her to vacate the premises and deliver vacant possession, failing which you can file a suit for ejectment to eject her from the property since she has occupied the premises illegally and termed as an illegal occupier. 

Since your father had bequeathed his property to you by registered will so you became absolute owner of property and has right to dispossess your sister through due process of law.Issue legal notice to your sister and ask her to vacate the property.If your sister do not comply with notice then file suit for possession and also claim mesne profits for use and occupation of property.