Mm, yes, but Hydra's father also gave her an impossible task - convincing Bellatrix that marrying Justin was a good idea. I can't imagine any circumstances where she would have agreed to that. I'm sure in her mind, Hydra will either marry Harry or no one at all.

I wonder if Hydra knew, deep down, that there was no way she could ever convince her mother to approve the pairing. Even suggesting Justin as a partner would have put him at risk. Bellatrix would have probed further, and might've even discovered that his blood-line had been fabricated. That would explain why Hydra took such risks - because she knows, at least on an unconscious level, that she can never really have what she wants. None of us will. Not until he's gone. Better to accept that now than cosying up to soothing delusions.