1/2 cup is just a general amount to start with for a small breed bunny. If your bunny is the Harlequin breed(not just the color of a different breed), then they seem to be more of a medium size rabbit, so you may want to feed closer to 2/3-1 cup a day. After your bun has been doing good for a few more days, acting normal, and poops are normal, you may want to gradually increase the amount of pellets each day, until you get up to the 2/3-1 cup amount. It's really going to depend on your bunny. If your bunny grazes on pellets and hay all day, and doesn't eat her pellets all at once and eats a good amount of hay, then you could give her closer to a cup or more, to where she is just running out of them right before the next feeding time, because she would self regulate the amount she eats. If your bun just chows down on pellets, and won't eat much hay if there are pellets, then you do want to limit them so that your bunny will also eat hay. My bunnies were like that, and what I did was cut their pellets back to an amount, so that they ran out of pellets about 3 hours before the next feeding time, then they would have to eat their hay. I fed twice a day. Only if your bunny starts getting noticably fat or starts getting soft poops, would you need to cut the pellets back a little more. When she gets to be around 7 months old, you you will want to cut back on pellets a little more, to about 1/2 cup per 6 lb body weight. Then at a year old you will feed the adult amount of 1/4-1/2 cup per 6 lb body weight. It does vary with each rabbit. If your rabbit seems to put on weight easily, then you may have to go more towards the lower amount, or if your rabbit is very active and slim and doesn't keep weight on well, you may have to go with the higher amount. Just always keep an eye one your bunny to make sure that with the amount you are feeding, she stays at a healthy weight and doesn't get boney or chubby. It's just a bit of a balance act with rabbits. You just have to find out what works best for your rabbit, cause all rabbits are different.
It didn't seem like the pellets were the cause of the problem though. I would be more inclined to think that the cabbage was the culprit. So as long as you don't feed her cabbage again, she should be fine. You may also want to stay away from other cruciferous veggies, just in case she is sensitive to all of them. When she's 12 weeks, you can start introducing veggies again. Just start with one at a time and in small amounts and gradually increase, as long as there aren't any soft poops or stomach upset. Also limit sugary veggies like carrots and fruit as well.
