Bilingual families

So my husband and I are born from the US , but our families are from Mexico. We both are fluent in both Languages and our 3 year old is mainly an English speaker but we want her to be fluent in both. It's sad that in our families we have many relatives who can't really conversate with older relatives because they speak more English than Spanish which is not bad but I find it useful to know both languages and well. So what we have been doing is trying to teach her more Spanish fearing that once she starts school she will drop Spanish completely , but I also am torn when she is spoken too in English by others she seems a bit confused due to the differences in languages. I notice it more now since she is so talkative. So do have any families been through something similar? Should we stress in teaching her the second language or wait till she is older?