I would suggest Cabarete, it is filled with younger crowds and you are close to the beach.
I think she will have a lot of fun, as I had clients like year going there with 2 children 13 and 15 and they loved it.
If you need help with accommodation , do drop me a line at
info@sunnyvillaholidays.com or have a look at our website and I would be glad to help.
Godd luck and happy travels.