Direct database connection vs Web service for sharing data between 2 related applications

I'm working on a web application project in Java. Currently, it only has the user front-end. Any modification is done to the database(s) directly. It uses a combination of MySQL and MongoDB. Now, I need to create an administration panel for it. It's going to be pretty large with lots of analytics and stuff. So, I was thinking of making it independent of the main application. The problem now is, how best to share the data between the two independent but related applications.

So my questions is: would it be better to move some of the portions out of the existing app into a kind of web service or should I just let the new application (administration panel) connect to the existing database?