Both my Junior year and Senior year I went with friends.
My Junior year I made my friend go that had just lost her mom a few months earlier. We went with another friend and the guy she was seeing - he drove us.

My Senior year 8 girls went together b/c no one wanted to take dates.
We had a blast both years and I would do it again in a heartbeat.

I moved to this county and one year around prom time I was talking with a co-worker and she said they were at a fancy restaurant and there were a bunch of girls in prom dresses eating and they must have been going to prom. "Can you believe that - they didn't have dates!" I said "uhhh - I went both years with friends" she replied. "pffft - that would NOT happen here - if you don't have a date you don't go!" I was like wth?!

I'm certainly not saying the girl that wanted to take her girlfriend should have lied about it - but I agree with Richard - there are other ways around it.
We had girls wear tuxes to prom and I graduated 16 years ago!