Aside from Abby’s computer skills, she also possesses a particular skill set that could be invaluable to Tony and Ziva.
Perrette’s character was a revered forensic scientist, capable of helping the couple identify their targets. However, rather than a regular slot in the cast, her role would likely be a special appearance. Considering the nature of NCIS: Tony & Ziva, she wouldn’t have a lab like the one at Navy Yard. Nonetheless, having this option for her NCIS comeback is better than having no option at all.