The fact she’s a no mark, works for him not against him. She’s not a threat. And to the extent that politics is all about spin, it will certainly be used against him pretty much like anything he does or doesn't do. But I think it'll be far more politically harmful for him if, post-VONC, he insists on being instated as PM and as a result fails to form a GNU, while the time runs out. He will be partly responsible for no-deal becoming reality while the Tories can play the blame game on him far more effectively.
Reminder that in the case of a VONC, first there's a 14-day period to form a government and win the Houses' confidence. Then there's a minimum of 25 days before an election. 25+14 = 39. If the VNOC doesn't happen this week (which it wont) then after the prorogation ends on the 14th of October there's no time left for an election before Brexit. If the VONC card is played then, it's either a GNU gets formed or no-deal Brexit happens.