What is the ruling on a suitor who came to propose to a specific girl, but her mother showed him all her daughters so he could choose from them?

There is no harm in a mother presenting her daughters to a suitor who has come to propose to one of them, as long as it does not lead to resentment or a loss of dignity. This is not considered proposing over an existing proposal because the first proposal has not been finalized. The suitor is permitted to look at all of them with the intention of marrying whichever one he finds appealing. Evidence for this is found in the statement of the man of Midian to Moses (peace be upon him): ﴿He said, "Indeed, I wish to marry you to one of these two daughters of mine, on [the condition] that you serve me for eight years."﴾ And in the action of Sa'd ibn Ar-Rabi' with Abdur-Rahman ibn Awf, when he offered him one of his wives to marry after he had divorced her.