How long is the charity ride going to be?

I basically did what your friend did

I was way too scared to go into an LBS alone so i bought a $300 bike from a sporting goods store. (They offered to let me test it by riding up and down the store aisles, which i declined) I had to walk up a LOT of hills in my neighborhood at first. But I rode once a week, learned to use the gears, and LOVED my 15mile charity ride. At the end, I had the bug to ride more, so i bought a better hybrid afterwards. I think my cheapie bike was actually a good thing for me because everything seemed so easy afterwards.

Your friend is lucky because she has you to teach her how to use her gears. If you are willing and able to ride slowly with her, I think she'll be fine on her cute pink bike I'm not sure I could have been convinced to spend more on a bike in the beginning considering I had no idea if i would like riding.