Eating healthy, low calorie foods like veggies, lean protein, fruit, nuts, seeds, etc will not harm your baby; they will help make her grow strong and healthy. As long as you eat enough calories to keep yourself healthy, your baby will be fine.
And don't forget to exercise every day. Now that spring is here, you can put your baby in her stroller and take a nice brisk walk every day. The fresh air and sunshine will make you both healthier and the exercise will help you build muscle that burns fat.
From what I've researched, it's not advised to go lower than 1500 a day for breastfeeding moms as it may lower your milk supply if you go even lower. But I think it still depends on the person. There's also a research about great amounts of toxins from stored fats being released into breastmilk if you lose too quickly. However, to be on the safe side, you could try starting on 1500 a day. Your BMR may be a lot higher than that. Breastfeeding alone burns 200-500 calories. If you're exclusively breastfeeding, you may be at the 500 bracket. See if you could lose pounds after a week and base it from there. Just increase your exercise if you wanted to lose more but don't want the risk to lower milk supply.
I breast fed for a year, very little fresh tastes of food for baby and was back to my my pre-pregnant weight in 1 year.
Do not lower your calories!!! Eat whole, high protein foods. You can worry about losing weight later (chances are you are gradually without trying anyway) working out is always a good idea, but don't push too hard or the stress can effect your milk supply. Remember to drink as much water as possible and eat as much protein as you can, you are building your baby's muscles and baby needs that to grow strong and healthy. Above all, remember supply and demand! If your supply dips for any reason it does not mean "you are drying up" (that does not happen ever unless you stop or supplement with formula) it means you need to add more frequent feedings. A baby can never be overfed or get fat off of breastmilk. For any advice or questions on breastfeeding and working out connect with "This Milk Matters" on facebook or Google it! Congrats and keep being an amazing woman with an amazing gift of milk.