If I were tickled to safeword, I wouldn't think the ler should feel bad AT ALL. Quite the contrary -- I would love them for it LOL
I don't think safewording is something that should make the ler feel like, oh damn I went too far. A safeword is there specifically so you don't go too far, but just far enough. You can't be expected to know that your lee has had enough, if they haven't had enough 🙂 This is, of course, when safeword = enough.
As far as do they want to be pushed past their limits, that's definitely something you'd want to set up ahead of time. If I wanted my ler to ignore my safeword, because I wanted to be pushed that far, I would tell them in the beginning, when I safeword, keep going. Don't stop until you want to (or the situation becomes unsafe -- obviously). I wouldn't ever think you should guess - okay she safeworded...does she want me to keep pushing?? Very dangerous gamble.