I really feel you on this, having a preterm baby makes every milestone feel so much more loaded to watch. Since she was born at 33 weeks, her adjusted age is actually closer to 3.5 months, so the fact that she is already rolling at all is honestly quite impressive. Babies at this stage do not roll on a fixed schedule, some days they just do not feel like it, so inconsistency is pretty common and not automatically a red flag. That said, because she is preterm, it might be good to bring this up with your PD at the next visit, just so they can track her development against her corrected age and give you proper peace of mind.