you said " I’m afraid she may be a bit underweight from being depressed about losing her. But she still eats though." that is the statement that concerned me. If she's underweight due to what you call depression, do not breed her.I know, but she isn’t underweight, she’s eating. What I’m trying to ask is it okay to breed the two even if she’s about 4 1/2 to 5 lbs?
I would NOT recommend breeding her to your bigger buck. It's not worth the health risk for her. And at five years of age, it is riskier for her to give birth.