Which pattern size should I get?

My daughter is 3 years old and wears a size 4T (she is tall and has broad shoulders, but is only 31 pounds). Height-wise, she is tall enough for the size 5. I'm not sure if I should get the pattern size 5-12 and risk it being a little big on her (how hard is it to take in?), or just get the 6m to 4 and know that she will size out of it within a year. I'm leaning toward just getting the smaller one and adding extra length, but I'm not sure. BTW, this is for a Christmas dress. Any advice would be great. Thanks!