When a cat urinates a on a new baby's things, is this supposed to be taken as a threat (or maybe just jealousy)?

My husband and I have a new baby (3mos.) and have two inside cats. When we brought the baby home, one of them began staying underfoot constantly and then jumping up next to us when we held the baby. We tried to give her extra attention and encouragement and thought we were doing OK until she crept into the baby’s room and peed on one of the rugs in his room, then the next night on the baby’s clothes themselves. We’ve had problems with this cat showing her anger by having “accidents” in other parts of the house before, but my husband and I took this to be an act of aggression and put her outside. We feel guilty, but the baby has to come first. I hate thinking that she might have to stay outside permanently. Has anyone else had a problem like this?