I'm not sure what this poison is. Sometimes if the tooth is badly infected, there's some pus that may be expelled. If that is the case, antibiotics should be taken and the infection should resolve after the extraction. Swallowing it isn't necessarily dangerous but I wouldn't swallow it if I could help it.
A dental infection can be cause for problems such as swollen lymph nodes due to infection and possible heart infections on damaged or artificial heart valves. But if she's getting her teeth removed, the source of infection is removed and the swollen lymph nodes return to normal. The bacterial heart infection may need to still be treated after the teeth are removed. Your physician should be able to properly refer her to a cardiologist if there is an possible damage to her heart valve.
Thank you, Dr. Tsang, for your response earlier, it was helpful. So if pus is that possible poison that my wife is speaking about, could that cause problems concerning lymphedema/lipodema or heart complications? My wife has had plenty of rotten teeth pulled since 2006 and she has spoken about that poison (pus). She was healthy then (2006), now she's has totally flipped the script (if you know what I mean).