Wedding Announcement/Shower

My Brother is getting married and is having a small wedding of close family and friends about 75 people. It is going to be informal with a JP in a park and the reception will be at a restaurant. My Mom wants to give them a party or Jack & Jill shower to invite some of her friends that will not be invited to the wedding. It will be an informal pool party. What is the etiquette here as far as expecting gifts from people not invited to the wedding. What should the invitation say, Wedding Annoncement/ PreWedding Reception/ not sure. Please advise. Thank you.