Sorry didn't see this until today..
How did your daughter get with her GTT (not nice at the best of times, but when pregnangt even worse)
At 21 weeks she still got a way to go until baby is born, depending on the GTT results, it may well be that she's got to keep a very tight diet avoiding all the high impact sugars, and also limited carb intake per meal to avoid high spiking of her sugar levels, but the GTT test will show the reaction of sugar on her system... They may decided to introduce insulin in some form to help reduce spiking and keep the bg tightly controlled...
What ever they decide is the best ward forward for your daughter and baby, they will keep a very close eye on her from now on, tight eye on her blood glucose levels, and also they tend to implement a lot more scaning, to monitor the babies growth rate... They may well decide to induce the baby just before she reaches full term they do look at everything before deciding if and when to do this though...
Policy used to be that babies were taken to SCUBU for monitoring, and to be weened of mums insulin, not sure what the procedure is now, as my 2 were born at the beging of the 90's so this may well of changed..
If your daughter does end up using insulin, She does still stand a good chance of being able to stop using it after her baby is born, also she may well revert back to normal non-diabetic status, but will maintain an higher risk of becoming T2 at some stage of her life...