How could lying on my CV backfire on me?

They could ask you a bunch of questions about your previous work experience in the interview, and then what would you say? You shouldn't lie about that but you could still write it in on your application, just go down and maybe help your cousin one day so you can technically feel you didn't lie, and if they ask just give a brief description of what you did or saw her do that day and pretend like it was you. Like research. I live in California and getting a job here is hard. They want everyone to be bilingual and have tons of experience! So you have to find ways around it by knowing people who work places or just getting by on your Spanish skills, and whatever they ask for. I've known people who completely lied about being able to speak Spanish on jobs that ask for bilingual people though, lol. I hate interviews but I have a job now. :) Good luck!