I missed asking a cousin to my party last year. I invited her siblings and can't think how she wasn't on my list. She noticed, before the event, and it got back to me. I phoned to invite her and at first she said "sorry but they were busy that day" and then luckily, she relented and came along. I was mortified by my stupidity. We are still friends
Maybe you could invite the neighbour to something?
Last weekend, in Rutland, the first statue in Britain of the late Elizabeth II was unveiled.