She may not transport as there are many providers here in MN (and other states) who don't due to the liability. Its a grey area of knowledge for most providers and parents as well. If you have not been to many trainings, as a provider, you may be very confused on the insurance issue.
But every single training I have been to says without Commercial insurance policies, your "regular" insurance (whether they know you do Dc....or even say you are covered) can and likely will dispute such a claim if it were to happen. There job is to NOT pay out, and the argument on their part would be that if an accident happend while transporting DC kids, this was during the course of a business trip, not a personal one, therefore a business (commercial) policy should have been in place. Also parents can not sign anything saying they won't sue the provider, blah blah, holding them liable or whatever for the trips to preschool...anything of that nature.
Aside from the obvious inconvenience of transporting...having up to date car seats, a vehicle big enough to transport ALL of the DC kids, the required MN State Transportation Safety training certification...they also HAVE to take every child out of the vehicle when going into the building to drop of and pick up the child....unless a school official is waiting at the curb with the child in hand (as far as I know none operate this way..parents/caregivers are required to go into the building and sign children in and out). A provider can lose their license for leaving a child in a vehicle unattended. Consider this for a winter scenario as well. Lots of snowsuits and boots and in and out of a (??) Minivan, etc...
I am not sure why you would want your kids to go to DC on days you don't work (unless you pay for those days anyway)? If you have T/Th off...this seems ideal for a preschool 2 days a week situation, and daycare the other 3. I guess I am confused why you would need to change that (I guess I am assuming this M,W,F thing is your schedule now?) So why are you being asked to change things so much? It sounds too drastic of a change for your schedule...too much for a provider to ask to make things easier for her or to accomodate another families schedule (just my opinion as a licensed daycare provider of 14 years here in MN)
Good Luck!