We don’t know that Harvey is going with her. Joel just said Wendi and the boys. Just speculating, but in my opinion it could possibly be that she might want to get the boys settled somewhere where nobody knows them, in advance of the trial. Another possibility, in my opinion, is that she could be thinking she might be arrested and might want to place the boys with family. I think I remember hearing there is family in Texas, I remember that there was someone on one of the jail recordings speaking to Charlie.
If Wendi believes that she'll be incognito in Austin, then I think she has a surprise coming. This isn't the 80s, when you could move cross-country and no one would know who you are.
She's immediately recognizable and enough people are familiar with this case that the news will soon spread like wildfire. All her coworkers and all the parents at her kids' school will soon learn all about the Adelsons.