Her problem is that as the girlfriend of the second in line to the throne she attracts enormous press interest whatever she does. If she doesn't work then she is criticised, if she does work then there is the risk of her being constantly doorstepped by the paps and the ever present risk of compromising herself (in the way that the Countess of Wessex did by carrying on her pr work after her marriage)....working for her parents company is the obvious answer to both those problems - it means she has employers who understand her personal circumstances, avoids people callling her a layabout and means she can earn an income of her own. As to all this nonsense about partying - she's photographed when out because of who she is - but she's also a young woman in her twenties with plenty of friends who enjoys going out - in other words no different from hundreds of thousands of other young men and women who also probably go out and about every weekend whether to clubs, pubs, restaurants or parties!
Whether she and William marry or not is still very up in the air but she rarely puts a foot wrong and a lot of the unkind gossip that's appeared about her comes from some of the overprivileged, over indulged wealthy society friends that are aquainted with both William and Harry and either don't like her personally or don't like the idea of her.