Mum has given us "holiday" but we don't want to go?

My mother gets rung up by these holiday companies that offer her deals. She puts a deposit on them and then uses them throughout the year. She offered one to my partner and I but never mentioned money. Now she wants us to "use it up in a hurry" because it is falling due. The thing is that it is going to cost us $250 and it is really awful accommodation in a place we don't really want to go. We are trying to save and organise for a wedding at the moment as well and can't really spare the time or cash. The weekends at this place are crowded with tourists and we really don't want to go there. My mum is very insistent and will see through my excuses and get offended. Any suggestions?