I have quite some experience of living with flatmates, and I see the other side of this. There is clearly a need for a table, even in the op it's mentioned.
Said flatmate went out of her way to buy the table, arrange or maybe even do the delivery and/or construction herself and save amity the hassle of doing any of that.
Amity will no doubt use the table a whole lot during the year, eat on it, have parties around it, probably even have sex on it. I think the whole deal is worth around twenty pounds, and she doesn't even have to pay straight away.
I think *****ens and Mae are giving some bad advice here. JMHO.
Plus, your flatmates will think you are being a tight arsed difficult ***** if you cause a stink about it, and, in my humble opinion, justifiably so