Isn't Selenium basically a way to remote-control browsers from Python? I don't know how exactly Selenium does that, but most likely iOS Safari is not one of the supported browsers. If the communication with the browser is (or at least can be) done via network, you could perhaps control a browser on your PC from Pythonista on your iDevice, but that's probably not what you're looking for. You'd need to be in the same local network as your PC, and then you might as well run your script there directly.
There are ways to automate web requests using Pythonista though. The requests module can be used to communicate with the server (requests is much more straightforward to use than urllib2 from the standard library), and HTML can be parsed using Beautiful Soup (bs4). Those are third-party modules, but Pythonista comes with both of them included. Keep in mind that this is nothing like using Selenium - these modules work at a lower level than a full web browser, so you'll want to use them differently. Instead of trying to simulate the entire "journey" through the website, you'll need to find out which parts are important, what URLs you need to request and what response data you need.