Is a girl entitled to inheritance and a mandatory bequest after the death of her grandfather?

You have no inheritance from your grandfather due to the existence of a direct son of his who bars the granddaughter. This is unless the grandfather made a valid will in your favor within the limit of one-third (of his estate). As for the law of obligatory will (al-wasiyya al-wajiba), it is null and void.

If your grandfather wrote a fictitious sales contract for an apartment in your name, there are three scenarios: 1. If he gifted it to you during a death-sickness (marad al-mawt): It takes the ruling of a will, and you may own no more than one-third of the grandfather's estate from it, unless the heirs consent. 2. If he gifted it to you during a period other than a death-sickness, and you did not take possession of it before his death: The gift is not complete, and the apartment belongs to the heirs. 3. If he gifted it to you during a period other than a death-sickness, and you took possession of it before his death and acted as its owner: The apartment becomes your property and has no relation to the grandfather's estate.