This could be good. Or spectacularly bad. (I think we're too many hours in for 'spectacularly good'.)

On the bright side, if she's with Harry, all she has to do is say, "I have to go right now, check my journal" (i.e. "look for a post from me" or "look at who has written to me") and he can say "Bellatrix just summoned Hydra" without her telling him anything, because that's the obvious assumption.

(Or she could just tell him, which is apparently what happened.)