I understand your mum is in a bad financial situation herself but she shouldn't be pressuring you to go if you can't afford it. I do have to agree with other posters, though - weddings are planned months, sometimes even years, in advance so you should have known to save at least some money, unless you just presumed your mum would pay for you?
You need to start looking at your finances realistically and acting like an adult, if you can't even afford rent, why are you still spending money on visiting your mum at home? I recommend you get a job as well if you really are struggling that much. Time to prioritise.