If you Google "nutrition for pregnant women" you'll find a lot of good information. Right off I found this --->
Mayo Clinic, Pregnancy Nutrition and this --->
Pregnancy Nutrition and Health.
As far as losing weight in a safe way while pregnant, she really needs to talk to her doctor about that. I would think it's possible, so long as what she eats is healthy and well-balanced, and meets her caloric needs along with the baby's. According to what I found on Google, during the last 6 months of pregnancy, she would need around an extra 300 calories a day (that's in addition to what she would normally need). So I'd suggest that you calculate her TDEE for a weight in between her goal weight and actual weight, and add 300 calories to that.
As far as any kind of workout, it's probably not a good idea to start her doing anything new when she's pregnant. She
can walk, however, so I'd recommend that she walk an hour a day (building up to it slowly of course). Walking will also help her keep/gain strength she'll need to deliver the baby. Again, she should check with her doctor.
