Can a general demurrer be determined only upon the facts supported by the amended complaint?

Although both parties cite and rely upon the rule a general demurrer may be determined only upon the facts supported by the allegations in the amended complaint, unconnected with extraneous matters (Griffith v. Department of Public Works, 141 Cal.App.2d 376, 381, 296 P.2d 838), defendant asserts on appeal the insufficiency of the complaint to support a cause of action premised upon an estoppel. Seemingly, the reason for this position is the fact plaintiff in the former appeal urged estoppel as a basis for her petition seeking permission to file a late claim, the consideration given by this court in our opinion on that appeal to the issue of estoppel as related to the merits of the case, and plaintiff's motion requesting an extension of the time allowed to amend was premised on a claim of estoppel which she sought to assert by way of further amendment.