Do I have a right to be mad??

I work part-time at a bank and this is the first time that I can honestly say I love my job. I take pride in my work and always make sure everything is correct and done on time. It's a small bank with only two tellers and a branch manager. The other teller is a girl my age and I am really beginning to dislike her. On more than one occassion the branch manager has had meetings to go to leaving the other teller to open the bank. I don't have keys or the code to the security system being I am only part time, but the other teller does and is expected to open up when the branch manager isnt here. Every single time the branch manager has a meeting to go to, the other teller is late leaving me standing outside with the customers. I call the branch manager on her cell and every time she has to come and open up, leaving the meeting. Then an hour later or so, the teller comes strolling in hung over. It happened this morning and she came in still drunk from last night. She made up a lie to the manager telling her that her car broken down on her way to work but the teller was in blue jeans and a wife beater with no makeup on!!! I am pissed!!!