I don't know her detailed policy views, although if J-Street supports her, chances are her views would be at odds with mine.
But I did see an interview with her in Jewish Insider from last July which included this section which sounds like J-Street:
When asked about the Trump administration’s current push to secure the “ultimate deal” between Israelis and Palestinians, Slotkin push for active American involvement, “The only way that this gets done is through strong American leadership. The only way that the two sides even come to the table is if the U.S. with a very strong lead convenes pushes both sides to make forward progress on the issue. But, if the parties are unwilling to come to the table, then unfortunately we are in a number of additional years with the same conflict with the same problems.”
Now, compare what she said with what has been happening the past few months. The US is pushing both sides to come to the table - and it is putting pressure on the Palestinians that has never been put on them before.
Which is what Slotkin wants, right?
I suspect not. When she, and J-Street, say they want the US to take an active role in pushing the sides towards peace talks, they mean to push Israel to accept more compromises. Their "pushing" of Palestinians is more like "if we get more concessions from Israel, will you pretty please consider negotiating then?" to which the Palestinians always answered "No, you need to get a few more."
Slotkin's Twitter account has nothing to say about Jerusalem being the capital of Israel, which seems to mean that even if she agrees with the position, she will not mention it because she wants campaign cash from Democrats and J-Street which are against anything Trump does, even when it makes sense.