The school personnel are most likely recommending kindergarten because your daughter's delays are fairly large. They probably feel that it is unlikely that one more year of preschool will allow her to catch up to her age-level peers. Most educators would probably recommend that a child in your daughter's situation move along with children their same age, but with appropriate assistance. If you try to think several years ahead, will you feel comfortable if your daughter is always grouped with children one or two (or more) years younger than she?
In most states, the school principal is given the authority to place a child in the most appropriate grade level or setting. You are considered part of the IEP Team for your daughter, however, so you have the right to have input into what will be most appropriate for her.