Your daughter's intentions are admirable. But she's only 2 years old and doesn't yet understand the consequences of some of her behaviors. This is completely normal for a child this age.
Rather than having her leave the other children alone, provide her with more supervision and guidance. Remember that toddlers are often confused by verbal instructions that are complex, vague, or abstract. Telling her "Be gentle!" is not likely to do much good since the concept of "gentle" doesn't make sense to her yet.
Make sure you're standing next to her or have her in your lap when she's with a smaller child especially a baby. Stop her when she starts being even a little too rough. Praise her when she's gentle so that she's more likely to continue acting this way. She'll enjoy the extra attention from you and will start acting more the way you want.