Good instinct. A phone waiting for her on release day is one of the most practical things you can do, and there is no reason you cannot make that happen. Halfway houses allow residents to have cell phones, so once she arrives, she can keep it with her throughout her stay. Getting that communication line set up before she walks out the door means she is not navigating the first hours of freedom without a way to reach you.
Shipping a phone to a bus station for pickup is not a standard service most bus stations offer, so that specific approach has some logistical challenges. Most Greyhound and regional bus stations do not have a package holding service for passengers, and counting on a station agent to hold something for an arriving traveler is unreliable.
More practical alternatives worth considering. The first is shipping the phone directly to the halfway house. Call the halfway house in advance, explain the situation, and ask whether you can mail a phone there to be held for your daughter upon her arrival. Most halfway houses understand that residents arriving from incarceration need basic communication tools and will accommodate a reasonable request like this if you coordinate ahead of time.
The second option is shipping the phone to a FedEx Office, UPS Store, or similar location near the bus station or halfway house that offers package hold or pickup services. Those businesses are set up to hold packages for pickup by the recipient with identification.
On the phone itself, since it is a used device, make sure it is unlocked or compatible with a prepaid SIM card that can be activated without a contract. Prepaid plans are the most practical option for someone coming out of incarceration who may not immediately qualify for a contract plan.
Coordinate with the halfway house before the release date to confirm the address and their willingness to receive the package. That one call removes most of the uncertainty.