Humm, 13 years between births... pregnant at the age of 38!?! This just sounds like a mid-life crisis or some such thing. This, by medical definition, is a high risk pregnancy. I really hope, that if she is pregnant, it all goes well.
I feel bad for the younger one, as they will not have much of a traditional relationship with their older sibling. Friends of ours had an "oops" kid that was also 13 years younger and the two of them hardly grew up together. When one started 1st grade the other was off to college. I have seen gaps of as little as 8 years make the divide irreconcilable.
My estimate, given her age and previous pregnancy, is that she will attain about the same bust-boost and be more protuberant in the belly, butt, and thighs. I see her packing on considerably more weight and not shedding as much afterward. Overall, she will end up a solid BBW size, some noticeable breast ptosis and slight abdominal droop. After a short while, pushing 40 she will slide out of the profession to "spend more time with my family".