I agree with those who say that rather than a camp, she needs to be home with her new parents and sister, having one on one play dates with other kids. If you don't know lots of families with kids this age, seek out parent-and-child classes that meet weekly, like Music Together; Kindermusik; Gymboree; and others where the parent attends but other kids are there too.
About camps: Bear this in mind: Camps can be very chaotic. Some have "counselors" who have little or no training in dealing with kids her age (others do, but if you end up with counselors who are not good with/trained with kids, she could end up with a bad experience); and many kids in camp around here are in camp because it's day care while mom and dad work - not because the kid wants to be there and enjoys it. I say this as a camp counselor, too!
I don't know if you work and wife is at home or vice versa, or if you both work full-time and need camp as day care -- I hope not the latter at this point, since children this young just adopted could use a summer just with a parent. If you can, take a lot of time off work, as much as possible, to bond with these kids. Are you and they getting any kind of advice, counseling, adjustment help from the agency that helped you adopt them?
Are you hoping that camp might help her with language and socialization? It could, but truly there is no rush for her to be in such a large group for the entire summer. She needs time to move gradually towards preschool and a full summer of camp (and it likely would be several different ones stitched together, at this age -- there are few all-summer camps for kids this young) is going to be stressful for her amid the change she's already experiencing.
Also, do you already know what preschool she will attend in the fall? If so, it would help her a lot to do some activities there over the summer! She will be more familiar with it and more comfortable there if she has at the very least toured it or played on the playground there a few times over the summer. Some preschools do "camps" that are not all-summer ones, or they do days when parents of kids entering in the fall can get together and bring kids to do an activity there over the summer. Ask the preschool about it now, not later, so you can book it. (If she does not already have a reserved spot in a preschool and you're just planning to send her but haven't picked one -- I hate to say it but you need to find her one ASAP. Slots fill up VERY fast and well in advance of fall. Preschool is a great idea for her but not full day, five days a week -- ease her in, with maybe three half-days a week or so.)
BRAVO to you and your wife for adopting.