My New Born is 6 months. I learned the hard way that travelling more than 2 hours each way to events in the UK was too much. He's a pretty chilled baby, but babies are still disregulated, can get colic, tummy & sickness bugs, separation anxiety or suddenly ill without notice. When we've taken him to events, I didn't enjoy them because I was anxious because of baby related things. Not saying you would be, but it's a possibility to have in mind. When we travelled abroad, he woke up every hour because of the unfamiliar environment and was clingy and wanted me, not my husband.
In summary, I can hear the love you have for your friend, but what she is asking you to do is likely to compromise yours and baby's wellbeing. Your mum being there may mitigate that somewhat, but if that's now not an option, the stress she is asking you to bear, is too much.
It's not her fault you have a family to think about, but it's your responsibility to make sure both you and baby are fine. She is prioritising her wedding (understandable to an extent) but you must prioritise your wellbeing. Even now, with our bubba being 6 months, the arrangement you describe gives me knots in my stomach.
Your friend knows you love her. Perhaps suggest doing something with her in the UK/where you are based after the wedding?
I know your husband has offered, but that's taking another resource out of an already strained, sleepless household. What you need, in my view, is an external resource (I.e., not your immediate household) taking that burden on your behalf. Your mum sounds perfect for that - but, it's unfair to have her stay elsewhere. In addition, you don't know how your hormones will impact you by then. Please look after yourself. This is coming from someone who tried to Please others and made a lot of premature effort and ended up feeling burnt out with a newborn. I had to rethink what I could say yes to. Sometimes I had to give nos I did not want to give, because I needed to.
I am so sorry you are at these sort of crossroads. So much changes when you have a baby, unfortunately, this can impact the closest of friendships - but in necessary ways as you adjust to new responsibilities/dynamics.
Good luck with it all x