Husband keeps getting a friend request from girl

To keep this short, there was this girl my husband used to (before he knew me) be really nice to and flirty to and she used to be the same way. Well, my husband and I have been married 3 years together 6. They were never dating but "flirting" about 7 years ago I'm assuming. So about 3 years ago right before we got married she sent a request. He declined and told me this girl may try to add me because she's friendly and used to talk to him and tried adding him. Then about a year layer(2 years ago) she sent him another request and a message that said something along the lines of "do you remember me how are you" completely harmless.. he replied something like "yeah I remember you, I'm good just got a better job" and then she said "is that your gf in your picture" and he said "that's my wife" and she said "she's pretty" and he said thank you and that was the end of that. I am guessing she blocked him because when he went to decline later that night the request and profile was gone.

Well now(3 years into our marriage) she sent another request. Didn't message or anything. My husband said he wants to message her and tell her politely to stop but I say he is over reacting and I appreciate it. But now I'm thinking it's a good idea. I don't know if she's trying to hit on him or what. I have guys on my Facebook and he has girls but he volunteered me the info about their past. I just don't know, I told my husband it's up to him but don't say it rudely because she may think it's a jealous wife that got ahold of his account.. when I don't look at his stuff lol

Thank you.