I think what she means is there is more clinical type jobs for LPN's in like dr offices than RN's which is true. However, you are limiting yourself to jobs as an LPN. You will make more money as an RN and there will be more opportunities to pick from.
There are many RN jobs that are normal 8-4 hours. For example, there's school nursing (you may need an BSN for that though), staff educators, management, hospital clinics, cancer infusion centers, many dr offices still need/want RN's, urgent cares, radiology nurse positions, OR, contact centers, cardiac cath labs, home health, etc. However, you MAY have to work 12 hr shifts in order to gain experience for those positions.
You already works as a medical assistant in a pediatrician's office so if you pretty much know what working as an LPN in that type of setting would entail. (Pretty much what you're doing now.) If you're happy with that and know that's what you want then go for the LPN and then later if you decide you want something different or more you can go back for your RN.