UserGuiding does not support iFrames since it's not possible to load the UserGuiding script within it. Therefore you won't be able to highlight elements inside that area through the Chrome Extension.
Guide steps (tooltip/input field) and Hotspots require a specific HTML element to be linked to, and if your elements are inside an iFrame, our tool can't reach them.
Thus, you can only highlight the areas outside the iFrame; or create other materials that do not depend on HTML elements such as Guide Modals, Checklists, Resource Centers, etc.