Thanks for your enquiry.
I take it that your father and step mother held the property as joint tenants? (meaning that on the first death, the whole of the property passes to the survivor)
I take it that they did not prepare Mutual Wills. This is different to "mirror Wills" which are merely identical to each other. (For wills to be treated as mutual wills there has to be an express agreement between the two testators that both wills will be irrevocable and will remain unaltered. Normally such an agreement will be incorporated into the wills of each testator).
I look forward to hearing from you.
Unless they made Mutual Wills, your step mother would have been free to change her Will and she would not have had to have given you notice. If they had made Mutual Wills, the contents of the Wills are binding, so you could sue your step mother's Estate if she has gone and altered her Will to exclude you. You do therefore need to find out if they were Mutual Wills (if you can find your Father's Will, it will say if it is a Mutual Will). If the same Solicitor oversaw the new Will, this implies to me that they were not Mutual Wills. Otherwise, the Solicitor would not have prepared a new Will for her.
If they were not, I'm afraid there is little you can do to contest her new Will, unless there was some formal agreement between you and your father and step mother guaranteeing that you would receive a share of their joint estate and in return for this guarantee, you carried out an act to your detriment in the expectation of receiving your due share (eg you cared for them or maintained and repaired their property). I doubt this happened, and if so, I think you would be wasting your time in taking any action.
Sorry this is snot the answer you were looking for.
Thanks. I am guessing that is was not a Mutual Will, but good luck!
If I have helped, I would be grateful if you could rate my answer, so I can get credited or my time.