May I ask what web browser you are using?
No matter which one you're using generally CTRL+Num Pad Plus will increase the size/magnification of a web page being displayed and CTRL+Num Pad Minus will decrease it. I have seen many people accidentally reduce the magnification on a webpage or webpages they visit frequently and if they're blind or vision-impaired and not literally looking at those pages it makes no difference and, of course, they have no way of knowing it's even occurred. In addition, most browsers can and do remember how you set your magnification for any web page you visit and when you visit it again it immediately applies those settings.
Most browsers also support a way of doing an instant "jump to 100%," that is, normal size on a given web page, but how that's done varies.
If you're in a pinch I suggest that your sighted helper try CTRL+Num Pad Plus to bump up the size that the page is displayed in. Each hit takes it a little bit larger.