why don't you ask if you can attend the ceremony too, as that will not cost extra?
I am sure they will be flattered that you appreciate that the point of the whole day is their union - not the food, the party, the gifts, the 'politics' of who goes to what bit... etc
like has been said, she was ''a woman from work'' so not like your best mate - look at it like this - would you buy her a meal that cost �60, just to be in her company...?
no, probably not, so why should she for you?
we all have friends that we see often and enjoy their company, but unfortunately people are expect to feed their cousins and aunties and uncles, whether they see them from one year to the next or not - and that costs a lot.