Hi
Though a partition suit can be filed by sister, you need to see whether the properties she is claiming are ancestral or joint family properties.
Also if the properties are self acquired properties of deceased elder brother , the sister's claim of these properties being joint family/ancestral be dismissed by the court after trial.
Also since there is a claim by sister, you should use this opportunity to prove the will at court by calling the witness to depose before the court.
It appears the sister has made a false claim to grab these properties, but her ill intentions should be proved at trial and after your victory in the case you can claim your legal battle costs from the sister