In the case of the handbag, there may have been some personal significance in the bag itself (perhaps her bf bought it for her), or in some of the belongings in it (family photos etc.)
It may have been the thought of having to replace all the bank cards and the risk of money being stolen and having to replace her phone if that was in it too (all those numbers... plus old texts, photos and everything else in it)
It may also be the shock of realising that some malicious person has taken your belongings. It's not a nice thought and nobody likes being picked on and made into a victim. No matter how random it was, it would still feel like a personal attack at the time.
That's only if your bag contains the basics (wallet and phone). If she had all her makeup, ipod, kitchen sink in there too, then that's going to be a very expensive and time consuming pain to replace.
Sometimes I find people overly dramatic, but I can understand completely why your friend was devastated by her bag being stolen. I don't carry much in mine, but I would be very upset if it was stolen on me. Also, if my friends were less than sympathetic, that would probably make me feel worse (not a dig at you, just saying).