is it normal to suddenly start lisping at 3yrs?

[lfp2n]

DD is about 3 yrs and a month and has pretty average articulation/vocabulary abilities. Thre's still some consonants she cant say etc, but 's' has not been one of them. For the last 18 months she has said 'yes' very clearly and correctly sounding the s until last week. She now just says yeth all the time. DH keeps correcting her and saying 'its yessss like a snake', but I'm not sure if it would be better to ignore it and hope she self corrects. Is this normal, would you correct her or just leave it,

Lucy DD 3/03

[ellies mom]

I would probably ignore it for a while. My DD went through a stage where she would sort of stutter the last letter of some of her words. It was a little unnerving at first but it turned out to just be a phase. I'd give it a month or two of just letting it be, and see if she moves pass it.