Honestly, she may not even like the taste at this age. It is not like the milk she is probably used to drinking. You could allow her to try it to satisfy her curiosity and if she likes it give it to her sometimes. I doubt it would have any negative effects for her. I wouldn't go out of my way to make enough for her to have regularly though which for me would have stressed me out about having enough for baby and the older one. You can also help her feel connected when you're nursing by letting her "nurse" a doll near to you when her lil sis nurses. My DD and DS helped me pump the other day using a manual pump LOL. They just want to be a part of what is going on. I even let them drink out of some of DD2's bottles when she first started to have pumped milk in a bottle. They wanted to feel like they were still my little babies, too. They chose to have milk or orange juice in the bottles but they felt special and it lasted about 3 days and they wanted regular cups again. So, I'm willing to bet she just wants to feel special and little and loved and cared for the same way she sees baby sister is.