Don't worry bro, she can come here in US any time any date until her visa is valid. even i had this issue in my past. i thought that my parents must enter US before 6 mths for first time and then 2 can be anytime but the reality is what i share you above. Yes, they can come within anytime till the visa is valid. they just need to have something to say at the port of entry on their visit to US. take it easy..