Venus, 35, was fined $5,000 for not talking to the media after her surprise first round loss to Britain's Johanna Konta on Tuesday.
Serena, who cruised past Hsieh Su-wei into the third round on day three, said she had been watching television when her sister lost but has no reason to believe it would be the seven-time Grand Slam champion's Melbourne farewell.
"From what I assume, yeah, but I don't really know," said the defending champion when asked if her sister would be back.
"I would assume. She's never mentioned anything about not being here, not competing."
Six-times Melbourne Park champion Serena, who is also playing her 16th Australian Open, said having family around on the tour is a real bonus.
"Having someone there that understands the joy, the highs, the lows, the pain, is unique," she added. "It's not often in sport, but when it does happen, it is really something special."
Serena said she would be tapping up her sister for information about her next opponent, world number 69 Daria Kasatkina.
The Russian teenager, playing as a wildcard, upset Venus in three sets in the opening round of the Auckland Classic warm-up tournament two weeks ago.
"I don't think it's gonna be easy," she said. "Any time someone is beating Venus they are more than likely playing really good.
"So I definitely will be ready for that. I obviously will ask Venus what she thought of the match, and I'm sure (coach) Patrick (Mouratoglou) will know everything about her match and stuff. He's really good at studying."
IMAGE: Venus Williams of the United States reacts in her first round match against Johanna Konta of Great Britain.
Photograph: Ryan Pierse/Getty Images
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