First of all, NO one ever has a RIGHT to inherit. If someone writes a will and gives away property before death, that's fine, and is done all the time.
However, if your mother truly had dementia when the gift happened, there MAY be an issue as to whether she had capacity to make that gift. Such a case will be very expensive to pursue even if the facts support it, and you will need a lawyer and medical evidence. If the property is not worth much, the thousands or tens of thousands you will spend on a legal battle with not be worth it. If the assets are worth over let's say about $20,000, retain a lawyer immediately. Bear in mind cases like this will destroy families so think hard before pursuing it.
