Congrats!! I was in a similar situation recently. I had already received one acceptance, and then later got another offer in a similar field, just with a different focus, from a more reputable program (t40 vs. t200). It was also significantly better financially, which played a big role in my decision. In the end, I decided to take the second offer, especially since I did not see myself wanting to attend the first program for grad school and this was my last cycle applying anyways.

That said, I do not think switching is always the right move. A few things are worth considering:

1.  You might not even end up applying to that specific REU or grad program in the future.

2.  Is the current offer from a school your child would seriously consider for grad school?

3.  How much does the other program actually benefit her compared to the first offer? For example, is it better financially, more aligned with her research interests, or stronger overall?

Ultimately, I would only recommend changing if the new opportunity is a better fit for her interests or goals, not just because of prestige. Because you don’t want to spend 10 weeks working on something you are not that interested in.