Sibling Paid Parent's Home Off From When On Good Terms, After 30 Yrs Feelings Changed And Is Claiming Entire Inheritance Is Hers Now

I have an elderly father and concerned about when he passes. He's stated he's leaving the house to equal shares amongst all children. I'm ok with that though one sibling is claiming she will sue us for entire amount because she is claiming she was the one that paid off the home after she got money herself. She helped significantly and it was a gift back then to my parents when they were on good terms.
It's almost 30 years later and she had squandered her money she gold digged from a man. She's also a drug addict and alcoholic. She's claiming she will never let us have any portion because no one is on good terms with her. And will just keep us at bay through legal battles. Though, none of us are interested in fighting due to cost. She's the only combative one.
- Are there any legal claims to this? The home has almost quadrupled and it's in the Bay Area so over 1million by now.
My father's will does state if any of us disagree, we can sell and still get equal shares amongst us 3.
What can I expect after he passes?
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