She seems to always use her basic hunting bow rather than the enchanted glass one I gave her. Any way to fix that on PC? Thanks.

You need to take any hunting bows she has hidden about her person away from her. I think this can only be done through the console and the method I use is (with the follower "selected)

getitemcount 0010e2dd
This will tell you how many bows he she has

removeitem 0010e2dd #
where # is the number of bows as discoved above

Close the console and the folllower will now use the bow you have given her

I'll try it, thanks.

Be prepared to keep her supplied with arrows. Once you remove the hidden bow, the never-ending-arrow-supply bug is also removed.
If you just check every time you enter a new area (autosave takes place if you have that turned on), you can take away and then give back
whatever better bow you want her to use and she will use it instead of that damned hunting bow. She used up almost 100 daedric arrows before I
realized what was going on

it's a known bug on all follower, check out the mods abou follower, they are already some of the mods addressing this issue.

Or just add this to your game. http://steamcommunity.com/sharedfiles/filedetails/?id=10203

Turns out the problem is solved with the command line.

The bow will return when using the command line. Most likely when you dismiss the follower, or force the follower to level up with you.