D.S.
It may not work on a stain that old, but what I use for everything is Windex. Other BLUE window cleaners work too. (Purple or white doesn't work so it is something in the blue coloring.) I have been able to get dark green frosting out with this.
Try saturating it with window cleaner and then take a clean, damp towel and blot it. I put the towel down and step on it. Don't rub, it just makes the mess go deeper.
The other thing you might try takes a little nerve and I don't know if it would work or not, so if you try it, you are on your own. (Don't blame me.)
Here goes: When I was in beauty school I learned that to get hair color stains out you use hair color. The principle is this, "like takes out like." If the carpet was ruined anyway, it might be worth trying this. Fill an empty spray bottle with diluted kool-aid in the same color(at least twice as much water as usual.) Don't add sugar, just the powder. When it is saturated, spray it with window cleaner and blot as above. I believe it would work, but haven't had a reason to test it. If you do try it, tell us all what happens. The worst that would happen is a slightly darker shade of red.