how about getting a paint your own mug set and let the kids loose on it and give that to her from them. sorry im useless on gifts, how about a pampering voucher, back massage or something like that for your step mum??!!!
A ticket for a show? Or if you have brothers or sisters, you could club together and buy her a weekend away. From the kids – if you have a computer and printer, you could make up a calender for the new year with pics of the kids on it. Or you could get one of those digital photo frames – they start at about 50 euro in argos (you put your memory card into it and the pics come up on the frame).