It wasn't clear when that picture was taken.
Note, the vet's report said that the enlargement they thought they were seeing might be a normal variant for this species- it is also possible that there is some issue, but since that's not definite, it would not deter me from getting her necessary medical help. For all living things, just waking up in the morning carries a risk of death, if you know what I mean?
Snakes can get constipated without anyone doing something wrong, & without involving any big health issue- just like humans do sometimes. It doesn't necessarily recur, though an enclosure that encourages her to move around more would likely help to prevent recurrence. Constipation is not the big deal you're trying to make it sound like. Get this snake the help she needs, or find another responsible owner who will.
Bottom line- I've never heard of anyone, ever, that euthanized a snake for being constipated. (And I've been keeping many snakes for decades.)