Unmarried Sister VISA: 3 questions

[andheri]

Hello,

I have to get my parents and sister (20y, 2nd year Law) to the US for a 2-month trip on Visitor Visa. I am in H1-B. We have a grandmother (solely dependant on my parents in India) who will not be visiting and my parents work.

I have 3 questions --

1. Is there any thing special we can do to improve my sister's chances?
2. If rejected when should we reapply?
3. If my sister's is rejected, will it affect her chances later on for an H1-B or F1 when she applies in the future for a university?

[immihelp]

1. No.
2. It is difficult to get visa for young persons. Reapplying will not help.
3. Not for H1. May be or may be not for F1.