No, I don't think she can stop you if you are allowed to in the Parenting Plan/Divorce Decree.
I say do what you gotta do and if she wants to make a fuss, let her. She wont have a leg to stand on ...and honestly, it might not hurt to inform her that she might well end up paying your attorney's fees too if she takes you to court. Especially is you are the main financial provider, you have to go where the work is and to be honest the time you are talking about isn't that bad! The real question should be, will this move impact the kids' schooling? As in, are they going to have to change schools? That would be your one major road block, IMO.
FWIW: I don't think 30 mins is that far. My husband's ex moved one county over (even though she was supposed to clear it first but didn't, we don't like to make waves) and it was a 50 min drive for us and it sucked! We eventually moved ourselves closer to her (but still in our county) and it shaved a good 30 mins off our commute. We can totally deal with 20mins each way, granted in the winter it's closer to 40mins but we are OK with that too!