Should I say nothing or should I tell her where to go??

So I was with my boyfriend last night and everything was grand until I got home he rang me and was asking if had anything to tell him.. I genuinely had no notion what he was talking about, then he settled down and told me the whole story of my so called “friend” had text him saying that I’m doing nothing other than meeting the country and meeting people behind his back, which is 110% lies because I’m either with him or in school or work lol? But the past while she’s been weird with me telling me I don’t deserve him because he’s such a lovely person and all this and she’s never done putting me down about our relationship and making me feel my worst.. she told my boyfriend the only reason she was telling him this was because he’s a lovely fella and that he deserves someone older.. like what am I meant to do with her lol? Me and my boyfriend is grand but she is going down every single avenue to make us unhappy.. what should I do?