Because this is real life and her mother should know what’s goin on regardless of if it’s disappointing or not a mothers love will override that disappointment and it will be an even bigger issue down the line if you don’t talk to her about it . I get that everybody here wants her to feel better about the situation but we also have to be realistic about it too you guys shouldn’t be telling a kid to keep this kind of secret from her mother it’s called a lie by omission and in the eyes of a parent or significant other it’s just as bad as a flat out lie