Okay, follownhosea, I'll try and explain a couple of things. I don't know your wife, so I can only guess at what's going on there, but I can try and explain some general things about
the condition of bipolar.
1. Depression is nothing at all like a funk. The good times absolutely do vanish. Did you ever see Harry Potter and the Prisoner of Azkaban? Okay, I know it's silly-- but go with me. When the dementors come by, Ron says "It's like I never would be happy again." THAT'S depression. Nope. Nothing good ever did happen and never will again. You and I and anyone outside the depression can tell a depressed person that's not true, and it isn't true, but inside a depression is ABSOLUTELY IS TRUE. And it is, because it's a sadness produced partly by reality (she probably is sad) and partly by a chemical. And until you get that chemical imbalance treated, she's going to believe it.
2. That sadness is complicated by being the mother of an 18 month old. Being a stay at home mom is HARD. If she only gets out of the house on her own for 7 hours a week and that 7 hours is crappy, better believe she's gonna be in a bad mood. I too was a professional woman who chose to stay home. It was good for a while but the whole time it has been a struggle and the mood disorder absolutely complicates it. Staying at home with a baby is hard for emotionally healthy women, let alone those who have mood disorders. The boredom, the loneliness, the passion you feel for your child, the jealousy for your husband's career, the anger, these things all bubble up every day. Stir into a fine Guilt Stew. We are just now getting our 28 month old into daycare so I can go back to work. I'm good and manic. I can't take it any more. My husband and I fight nearly other day. It's been hard. and there's no way I could have done it without having seen a therapist every other week and sometimes more. I would have committed acts of violence.
I hope this helps you at least see a little more from her point of view, if nothing else. I absolutely do sympathize with you, just as I do with my poor husband. He's in therapy too, to help him deal with me, among other things.