Yes, Isabella was indeed listed in the baptism records of her children as "John and Isabella/Bella Neal/Neill", as if they were married.
Interesting that the first two - sons John and Michael - were baptised at St Mary's Portsea, where the parents were married as "Neal", but the two daughters at St Thomas Portsmouth, as "Neill".
Neither of the parents were literate and may not have known the proper spelling of their name, leaving it to the parish clerk to record it as he would.
They were both "of this parish" at Portsea, but if Isabella's first marriage were at Portsmouth, that's a much bigger search.