The actual font sizes can't be modified but there might be several workarounds around for her.
Open System Preferences / Universal Access
Or, in System Preferences / Displays then select the Display tab.
Try a smaller resolution.
At the bottom of that pane, have her select: Show displays in menu bar
That way she can access Displays from the Status Menu Bar (menu top right side of the iMac screen) without having to launch System Preferences for easier access to toggle the resolution back and forth.
Decreasing resolution "magnifies" the Safari toolbar font hopefully just enough to help her.
Message was edited by: Carolyn
I realize that this thread is two years old, but sometimes it helps to reply to help current and future browsers.
Small text and icons are, without a doubt, one of the worst things about the otherwise wonderful Mac GUI. The more modern our Macs, the higher the resolution, the harder the screen is to see!
Given that those with lots of disposable income are also often those who are older--and come with aging eyes--Apple seriously needs to address this. iTunes suffers from this problem, too. The reviews are too tiny to read comfortably on most devices-- whether Mac or the i-series (iPad, etc.).
Carolyn identified two of the main options to deal with this. Alas, though, the various solutions-- zooming in and changing resolution--have such major downsides that they really aren't a permanent, comfortable, easy substitute. One is forever scrolling back and forth, left and right, and dealing with grainy, fuzzy text. (And, yes, I've repeteadly suggested to Apple that they fix these problems. Hope others will, too.)
Whatever happened to the scalable interface that was being touted and rumored almost a decade ago? It would have meant easy increasing the size of all interface items.
Now, as to Safari, another solution, which doesn't help with the menus or toolbar, but does help with the text is to go to Preferences, Advanced, and check "Never use font sizes smaller than..." and select something large there. That will keep the crisp text, but prevent a web page from showing tiny text.
The other thing to do is to park the font size controls on the tool bar, where they will be easily accessible. Go to View, Customize Toolbar..., and drag the text size icon (small and larger A) onto the toolbar.
In any event, hopes this helps someone!