Yes, firmware can make a significant difference to when chatter appears, regardless of switch type. For example, there was a whole generation of Noppoo boards, back when they were still using 100% genuine Cherry switches, that would almost always develop chatter issues in a very short period of time. I suppose the opposite might also be true, with some makers doing a better job of debouncing. Various Chinese boards experimented with variable debounce-- so that you could have very fast response while your switches could handle it, and then slow things down a little as they aged-- but I'm not sure if it ever worked properly in anything that implemented it, and the feature seems to have gone out of fashion.
All that said, if you really hate chatter with a passion and a vengeance, and want to make sure that it does not occur regardless of what should happen to your keyboard during its life, you might consider a keyboard that has no contacts to chatter in the first place, but instead uses capacitive, optical, or magnetic sensing (the last of which AFAIK you can't get in a reasonably-priced currently available keyboard these days). If you want full-size capacitive with the ability to use MX keycaps for customization purposes, then you're looking at Noppoo or Royal Kludge. Various Bloody models (e.g. B720, B740) use optical switches, which your intended recipient might enjoy if she is a fan of linear action. Can't say I've seen one I liked the look of yet, though, and life expectancy of the emitters in their optical switches is unknown.