Bell, it sounds like your friend's fish had a case of "ick". There are treatments for that, you can find them at any store that sells fish usually...and Jilly has some articles on this site about taking care of sick fish and such.

Usually fish are all stressed out when you pick them up from the stores...especially bettas since they are only in those little cups and surrounded by other "challengers"...and....being picked up and jostled around alot by folks looking for a friendly fish. <img src="/images/graemlins/smile.gif" alt="" />
Finding a nice warm place for them and treating thier water with stress coat and aquarium salt when you get them home..and leaving them be for awhile so they can adjust...are good ideas. also keeping an eye out for illness as they are suseptable from being so stressed.

Introduce them to thier new surroundings slowly..float thier cup in the tank/bowl you will be putting them in, before you actually put them in the water. This is so they can adjust to the temp change(takes at least 15 minutes),then add a bit of the tank/bowl water to the cup and let them sit a bit. When you think you have given them enough time, tip them into thier new home nice and easy.

None of this guarentees no illnesses, but it sure helps!

Emg <img src="/images/graemlins/cool.gif" alt="" /> fish