One wonders what her contractual benefit to 100% sick pay is. If, for example, an employee has the benefit of six months sick pay before it falls to statutory sick pay (or a lower interim figure - often 50%), one strategy is to do as she is doing - go to the doctor, be signed off for stress, and push the onus back on the employer. It can take ages to get such an employee claiming this back to work - I've been there several times. The last one took 4 months of hassle before we terminated the individual. Even then one has to pay off the contractual notice period.
In my example we had a shirker who we bend over backwards to treat fairly and basically we knew the individual wouldn't come back and wanted to be fired.
Not I'm not suggesting for a minute that your daughter's case is not genuine stress brought on by a poor employer organisation - I'm sure it is based on what you say.
However this is perhaps a safer strategy than trying the constructive dismissal route. As I'm sure you know, one has to resign and claim constructive dismissal. It's a one-way street as there is no way back to the job if one loses the case.