First, she would want to get help for her self esteem problem (either in the form of counseling or working with a personal coach)
At 22 it is a bit late to learn how to be hones (but if she is doing the lying/manipulation) for attention seeking, she may re-learn proper ways to get that attention.
Of course, no matter what course of action she is to take, she must be willing to work on her behavior and self improvement. You can meanwhile encourage her to get the help she needs. If she is not willing, as a last resort you may want to consider a family/friend intervention in your home.
IF she gets defensive that is not because of what you did (rather her poor coping skill)
One way to approach it is to gently point out to her some discrepancies that her mom had made (if you're able to think of a time when mom promisesed her or told her something that was not true and especially if that disappointed her)
Another would be to just flat point out to her the discrepancy you've noticed and perhaps ask her if she meant to say something else (that way you're giving her an opportunity to save face and are not blaming her )
You are correct the lying is not per se a symptom of the depressive disorder (it is most likely a learned thing although some individuals with antisocial personality disorder would also lie)
Antisocial Personality Disorder for symptoms click here
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