Shelby did have anything to do with the design or construction of the Defiant, her and her team acquitted themselves with distinction, not in STAR TREK: FIRST CONTACT, but in DS9 "The Search, Part II". The Defiant was the first Federation vessel to successfully stand up to a Jem'Hadar task force and penetrate their defenses.
It's a shame Shelby was relegated to novels; if there was a past character from TNG which could have come back to the Enterprise-D to "shake things up"
again, it would've been Elizabeth Dennehy's outstanding portrayal of Shelby
. Imagine this: if Ronny Cox hadn't been brought in as Capt. Edward Jellico
(TNG "Chain of Command" cliffhanger), it would've been a joy to see a newly promoted Captain
Shelby come back and take command of the Enterprise-D. They probably could've used the same lines for Shelby that Jellico spoke. Imagine the tension between Shelby and Riker!