lurker here, but I had to reply to this.
Bettas are NOT solitary fish, and contrary to popular opinion (and Petsmart! arg), they do not enjoy being in small spaces. As air breathers, they are able to survive in small spaces, but you could also live in a 5 foot box. It just would not be comfortable. In fact, living in such a small space will make them prone to a disease called finrot, unless the water is changed completely every day. Bettas are also jumpers- thus, you need a tank with a top, preferably. Dried up bettas under your feet are not fun. Finally, a tank needs to be AT LEAST a gallon (water changed every 3-4 days) and preferably at least 2.5 gallons. Why? Because bettas are tropical fish and need water around 73-76 degrees. You can not safely do this in a margarita glass.
Bettas are wonderful fish. But they are animals and pets, just like dogs or cats. Thus, they need care. Honestly, I think they are a bad gift idea because people don't know how to care for them. If you do give her a betta, maybe print out some care info for her and include it. Like I said, bettas are great, and can (and should) live up to 3 years in your care. Just take care of them correctly.
FYI, I have 3 male bettas (the type you typically see in pet stores) and 6 females. I have been an avid betta raiser for about 3 years.
a great website is
www.livejournal.com/users/bettafishowners
or
www.livejournal.com/bettas