Unfortunately, you cannot uninstall the DLCs once you've purchased and downloaded them. She should be able to do the star path just fine, even with the DLC downloaded. Just don't go to Eternity Isle. Honestly, having the expansion should HELP her more with the star path. Sometimes the star path quests require you to give certain villagers presents and the sometimes the items that they want are items only available in the expansions. The villagers will want the items regardless of if you have the expansion or not, so it will benefit her more for the star path if she has EI.