Will she be sinful for lying to her friend—claiming the existence of an orphaned widow to collect money for her—due to her dire need, or will Allah forgive her?

The questioner's statement, "I and some acquaintances are collecting money for her," is a lie, and the general rule concerning lying is its prohibition, unless a person is compelled to it, or it is for the purpose of achieving a praiseworthy matter, or for securing a right. Since the question permits you to ask people for help when in need, you are not blameworthy for the lie you uttered. As for taking the aforementioned money, scholars have differed regarding an agent taking from charity for themselves. The fatwa permits it if the agent possesses the characteristic for which the money was specifically designated. However, piety dictates not taking it except with the permission of the donors.