Only 300 additional calories... is she gaining fat or just hungrier? With that that work load, she should definitely be able to eat more than before without gaining fat. If she is already eating small meals every 2-3 hours, is drinking enough water (which will help to feel fuller), and is _still_ hungry, she needs to change her food choices and go for more fibrous foods: steel cut oats, broccoli, cauliflower, salads, vegetables, beans etc. They will keep her feeling fuller for longer.
There's no set time for how long it takes for someone to get by the 'hungry' phase. Some poeple don't get it at all and some people never get out of it. I know many people who always get hungry if they don't have their usual meal or snack every couple of hours. If she's really uncomfortable with how she feels while weight training, she may be creating a body image she doesn't like as a result of the new regimen. The weight training is of course adding weight, but if she hasn't given her routine a chance to get into more fat burning, she hasn't started feeling leaner in addition to the new muscle, and that can be a very frustrating start - in addition to being hungry. If she is doing all those things and it is not helping, or if she isn't willing to make the changes, maybe it's just not a routine that suits her. It happens.

I agree with you that it is much healthier, especially for women with the threat of osteoporosis later in life, but if it makes her unhappy, it may not be worth it in the long run.