That is quite ironic and also it does not make sense at all to me, to be honest. When people talk about making their country great again, they are referencing a point in the past in which their republic was better in shape,.both economically and socially.
So if there was the case Kamala Harries started to go with such an inconsistent talking point, it would be in detriment of herself, as she is still in a position of power, in a position in which she could try to improve the quality of life of their voters and yet she would be only talking about the future (in the case she is elected president of the country).

I call it a rumor, she has better ways to appeal her possible voter than repeating what her rival says..