Advice please xx

So basically I met this guy at a festival last summer (he’s my guy best friends best friend not some random) and we got on really well but nothing happened between us but recently we’ve been talking a lot and we met up before Christmas in London as we live about 4 hours apart and London’s in the middle of us :/ basically we were gonna meet up again next weekend (side note I’m only 18 and still live at home) but mum said I wasn’t allowed to go. Now I don’t know if I’m being really unreasonable but in my eyes there’s nothing wrong with me at my age just getting a train to London which is literally just a direct train with no changes or anything and I pay for everything myself anyways. So does anyone know anything I can do or say to try and get her to let me or if I’m just being really unreasonable or if she is cos tbh I feel like I’m old enough to do these things but don’t want to argue with her if I’m just being really unreasonable😂