I am going to assume that if she hasn't taken the last 5 times she's telling you she doesn't need another litter. I would for sure take that as a major sign. If she's a small bitch under 5 pounds she shouldn't be bred to begin with. Has health tests been done on the bitch? ie...complete blood panel, bile acid tests, heart tests, and hips and knees? Again, I would take it as a sign she doesn't need another litter and I'd spay her and love her as a loving pet
Of course this is what I would do even if she were of breeding size and didn't conceive after the 2nd time. I wouldn't have bred her under 5 pounds either.
Donna