You have about four questions I think.
First, can your son sponsor his wife for immigration to Canada. The answer is yes. Since your son is a U.S. citizen, he can apply to the Buffalo office and must include his spouse (and any dependents) in the application. It doesn't actually matter where his family is living.
The second question is whether his wife can legally stay in the U.S. during the application process. Technically, the answer is no. She should leave before her visa expires to comply with U.S. law. However, I'll tell you that other 'out of status' individuals in the U.S. have immigrated to Canada. If she overstays her visa, that will not disqualify her from immigrating to Canada.
Third is whether she can go to Canada during the immigration process. I don't really see a way to do that legally, because your son isn't yet a permanent resident. If he were, he could sponsor her from inside Canada while she visited on a temporary residence visa. However, he's not so he can't and she can't.
What are possible outcomes? If your son's wife is detained or deported from the U.S. during the application process, it shouldn't affect her ability to immigrate to Canada. However, if she gets her medical checkup done in the U.S. and follow-up is needed, she'll need to go back to the same doctor. That will be a problem if she's detained or deported. Also, if your son and daughter-in-law are called for an interview, they'll be expected to be available for it in the U.S. If she can't attend, that will be a problem. And finally, overstaying her visa will affect her ability to visit the U.S. in the future.
So what I recommend is that she use her own best judgement. If she stays in the U.S., it is likely that everything will happen smoothly and the happy couple will be able to go to Canada. But there are some hazards that I think it would be best to avoid. I'd recommend she wait out the application process in Colombia.
