If it shows up as a valid connection, the bags should not have a problem. When it comes to IRROPS like the BOS-DTW flight being delayed, there can be a possibility of the bag not making it but the person will. No worries though, as DL would put the bag on another flight which could be the next day. They then would have someone deliver it to the place she is staying when it arrives.

I would pack at least one day's worth of clothes in her carry-on just in case of the above scenario. Once, my family had a delay due to weather flying SAN-IAH-FLL with a diversion to SAT as IAH was closed temporarily. When we landed, we had 15 minutes to "run" from the north side of the terminal to the south side as the departure had also been delayed. Our bags didn't make it, but we ended up having them delivered to my office the next day.