I am new here. My thoughts are as follows:
1. Venus was out 1/2 a year. The first tournaments back, she was rusty.
2. The losses she has had recently have been to players that didn't have a history of losing to the Williams. Sprem is the perfect example. She led 3-0 in the Berlin semi before Venus came back and won. She carried that confidence, and excellent play, into their match in Wimbledon.
3. The murder of their sister. This is huge. I recently lost a close family member, and things that were so important at work don't seem so important anymore. I have been told that will change in time. I am guessing it will take time for Venus too.
I think any talk of a slide is premature, whatever the rankings may say. Give her some time to deal.