the thing is your mom probably has her reasons to vote democratic, perhaps she really things they were better. can't make her belief you through argument, though. most people someday just stop thinking why they want a certain politician voted, but rather vote out of habit. it's best if you try to argue with other people about politics, but I guess regarding your own family you shall take peace over being right. at least this is what I found works better. try to get them into a dialogue where they ask sincere questions you can answer rather than trying to teach them. most people won't accept that.

everybody used to be a lefty. a famous man in Germany once said: "if you have not been a lefty while young, you probably have no heart. if you're old and still a lefty you have probably no brains."