If her parents are unable to financially support her visit then yes, she can include her grandfather's financial documents + a letter of financial support + his ITRs + proof of relationship.
IMO, it would be a lot less stressful if the grandfather pays for her visit.... that doing 'dodgy' deposits in the mother's bank account.... waiting for 6+ months.... and then reapply whilst hoping that the visa officer is not smart enough to figure it out
Regardless of who pays, she must be able to prove that she has at least her study ties to return home to