I can assure you that you can go from flowering back to veg once you see if it's a boy or girl. BUT you can't let it flower past a couple days once it starts to show.
Best way to pick out the strongest mother for clones.
When you put her back to veg, She will continue to show pre-flowers for ever, with no hermies. (at least not im my case) I kept her for 2 years in ebb/flow! (Clone Monster)