How long will it take for my toddler to stop getting colds?

My husband and I recently put our 21 month old in a lovely preschool three days a week at our church. She absolutely LOVES it, but has had three head colds within 2 months, the most recent one being the worst. I knew this would happen as she has never been in group care before. But, can someone with experience tell me if this will start to get better? My pediatrician's solution is to "stop taking her there" but I know that she is having valuable experiences with other children her age and like I said, she loves it. Will she eventually build up an immunity to these pesky head colds? Thanks!