First of all, often with stretch marks the best thing to do is to wait a while. This is because stretch marks, which form during pregnancy due to a combination of physical 'stretching' of the skin together with the action of the pregnancy hormones on the texture of the skin, will regress slowly after the pregnancy is over. This sometimes requires many months however. Initially the stretch marks will be wide and bright red or pink (or very dark brown in someone of darker skin tones); however, over time, they will tighten up and will fade to a lighter color that will blend in to the surrounding skin over 1 or 2 years.
If your wife feels like the stretch marks are not improving or does not wish to wait, then she could see a dermatologist
. There are various treatments that have been used to improve the appearance of stretch marks, such as prescription creams, as well as laser treatments and dermal abrasion. None of these treatments have been proven to work in everyone, but they are helpful for some people.
One final point: avoid over the counter creams and preparations that are marketed for stretch marks. These are just expensive and none of them have ever been shown to work!