"I have to believe that, and I know she has to believe that. We work so many years for these moments that she has right now, and I'm really happy for her," the 23-time grand slam winner told Yahoo Sports.
"I'm proud of her, everyone is proud of her. She's such an amazing person, and she's so nice, and she's been through a lot obviously, but we are always rooting for her."
Venus has overcome Sjogrens Syndrome and several injuries to reach her first Wimbledon final since 2009 and Serena believes her sister's triumphs inspire others suffering from the auto-immune disease.
"She's been through her illness, and she keeps fighting through it, and it would just mean so much, not just for her but for people who suffer what she suffers just to realise that this isn't, this doesn't have to be it," Serena said.
"You can go through what she goes through and still come out on top."
Venus has beaten Muguruza in three of their four meetings to date but will be wary of the world number 15 after the 23-year-old knocked her out of the Italian Open in May.
(Reporting by Aditi Prakash in Bengaluru, editing by Nick Mul)
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