I really think it matters where in Mexico you are and then if something bad is meant to happen to you, i.e. luck or fate. There is violence all over the world and in the cities we all live in, so I wouldn't be put off by Mexico in general.
However, there is a huge drug war going on in parts of northern Baja. Maybe that's what your mom was referring to? I think it was last year that the TJ police had their weapons taken away while the army stepped in because they were so corrupt. Around that time my Mexican friends were saying to stay out of that area because they were killing Americans at will because the FBI captured one of the major criminals there and they were mad at the US.
These days I think it's more a matter of being caught in the drug war cross fire rather than being a target as a tourist. TJ had 37 murders in 3 days a few weeks back, over 200 in the month of November I believe, etc. My brother has a house between Rosarito & Ensenada where a lot of insane stuff is going on right now (Mystery man blamed for gruesome Tijuana deaths - Los Angeles Times) but he drives there a few times a month without incident...so who knows. I wouldn't plan a TJ wedding anytime soon but I don't think anyone is doing that anyway