Yes she may petition her parents as USC.

This is the estimated time for USCIS to make a decision on your case.

Yes if no issues were addressed in rejection about forms.

No it should not as long as you can establish financial sponsorship for both applicants.

It depends on the case and court backlogs.

No specific minimum age but generally invitation letters are not required or assist with adjudication.

Yes you may each do without issue.

No you should either have GC or I551 stamp.

Yes you may do so without issue while case is pending.

That cannot have been your intent upon entry. Consult with an attorney for guidance.