OP, I feel your dilemma, especially if its a good friend and you'd like to be there at her wedding.
I hate going alone to weddings. I love the service but the rest of it,... Meh.... Always get sat with people you barely know on the "odds & sods" table, as everyone else is in couples making a neat 8 per table .. & they think "you'll just get on with their other single friends"! Argh...!! I do try but there's always some creepy single guy...
Not that its relevant to your dilemma but I learnt to say no after the worst wedding ever...
One of my close friends was organising her wedding in Italy about 3 years ago (before term time hols fining came in). Cost was escalating as it was all in a remote castle hotel in the countryside/ hills and was for 5 nights. It was a huge hotel so plenty of room. Then just before booking she said I had no plus 1 option, none of my DC were invited although I'm a SM (& my DC, her DD , my friend & I are all really close/all well behaved and DC excited about going!) and we couldn't afford a family holiday for god knows how many years if I went to her wedding abroad.... Not even an invite for my DD whom she'd promised could be a bridesmaid. Because she 'realised' I'd be too busy to play with my kids and it 'wasn't fair on them'... (For 6 days.... Whaaaat did she have planned?!!!). That made it so much easier to see I needed to politely decline.
(She eventually changed venue to uk as too few people could afford it, & they got married in uk,... Yup was not allowed a plus one- even though i said my I'd take my sensible DD as my plus one (there were other DC going) or another girlie friend of hers who she liked too - because I didn't have a boyf and 'it was more a couples thing'- and my friend and I even offered to pay her meal etc, and ...Yeah I sucked it up, went alone... was slapped on O&S table and "volunteered" into ferrying people to from venues including lift home to 2 drunk aunties on a 20 mile round trip! All with a babysitter to get back to before 11pm ... after 10 hours away!)
I don't like going to weddings without a plus one now on my invite. I say upfront, Fab please can i take my (middle preteen...) DD as my plus one. It's miserable otherwise and Letchy Uncles steer more clear if you are with your DD and making effort to entertain & shepherd all the other kids at the wedding too.