I think it’s a beautiful idea of kindheartedness on their part. Judaism teaches that there is no absolute prohibition against lying. Harmony and goodwill are of utmost importance and the truth may be withheld to achieve unity, friendship and peace.
In the scenario you describe it is not only allowed but actually an unselfish compassionate act on the part of your daughter’s friends. I think that it reflects an incredible sensitivity on behalf of the others who do not want to let the person in question feel like a “charity case” and yet they want her to come with them. Quite beautiful!
Permit me to add one caveat. As her parent, you should be aware of how she would react if she finds out that her friends are helping pay her costs. I think that there is a realistic chance she will discover this fact at some stage – before, during or after the trip. If you feel she will be embarrassed or react negatively to their kindness, I think you should try to discuss the entire situation with her in advance in a loving and positive manner and do what you and she feel is best for her.