pretty unlikely seeing Richard deposed here and I doubt who a girl would be an Elizabeth as Anne, Joan and Philippa are far likelier names.
I'd argue just the opposite. We know from Knighton's chronicle that the only reason Richard was
not deposed by the Lords Appellant in the meeting at the Tower on December 27, 1387, was because the lords could not agree on to whom the crown should pass after Richard was removed. The presence of a clear heir removes this problem entirely. The lords can now rather straightforwardly remove Richard and set up a regency for his son or daughter, as Mortimer did in 1327.
The boy would be married to Isabella, but Richard‘s heiress presumptive would marry Mortimer or Norwick not a French Prince
Richard had nearly as much contempt for Mortimer as he did Lancaster, so there is no chance he would arrange a marriage here. Norwich would be far too old, and the birth of a daughter would demonstrate that Anne of Bohemia was capable of bearing children and thus there'd be no one would see the girl as an heiress from the get-go -- they would expect a future child to be a boy.
I do think Richard would want a French match for his daughter. This may be acceptable to the political community in England for a time since, again, they would likely expect a son to be born in the future. But it seems to me that a revolt is guaranteed if and when it became clear that Richard was not having any more children.
Because Richard was NOT crazy and sign his lands over to a French Prince
Richard was not crazy, but he was politically inept. He was willing to divorce all of Aquitaine from the English crown when Charles VI suggested it -- wedding his daughter to one of Charles's younger sons seems like
exactly the sort of decision he would make, either oblivious to how unpopular it would be at home or simply not caring they his lords would disapprove.