What does it mean?
In an interview with Gayle King, Ivanka told her:
When I spoke to “60 Minutes” it was I think five or six days following the election. And I was processing real time the new reality and what it would mean … I realized that having one foot in and one foot out wouldn’t work. … And the reality is that it all happened very organically for me.
Best Answer
It means, simply, that being partially involved would not be successful. She's saying that she had to be "all in". Trying to be a part-time advisor to the president would lead to failure. If she was going to help her father, she had to commit to it fully.
I suspect she was making an allusion to the song/dance The Hokey Pokey where, at least in the US version, you "put your right foot in, you put your right foot out," etc.