My sister has completed BCA through lateral entry after 3 years diploma.Can she do MCA?or any other PG courses?

No, the first degree should be of minimum 3 years duration in any case. Any degree less than 3 years duration is not valid for higher education and public sector job. However, if a university fails to catch this, then she may be allowed.

Ashwani. do understand where she stands since most of the good companies hire only BTech or MCA. However, if she's creative, she can also consider going for Design and Animation. A good mentor and wise selection of courses with a good school, followed by diligent learning, would get you a head start