Hi, I am a dad to 3 beautiful children (1 girl - 4yo, 2 boys - 2 and 10 months). Their mother and I separated about 8 months ago, it was a mutual and amicable separation and we share custody of the kids 50/50. The relationship was over a long time before separation, realistically not long after we became pregnant with #3. We discussed everything at length and decided that it was for the best to separate, rather than staying together 'just for the kids' and ending up hating or resenting each other. In truth we grew apart and our lives were heading in different directions. All seems to be going fairly well after a few months of adjustment to the new arrangements. The kids are happy and thriving.

I have recently entered a new relationship with an old friend. The relationship is progressing well and we are both very happy. The kids have known M since they were born and are very comfortable around her. My ex initially had a few doubts about M coming into my, and the kids lives, but has grown to be comfortable with the way things are progressing.

Which leads to my question:
M isn't sure what she should be introduced as. She doesn't want to be known as "Dad's Girlfriend" but doesn't feel that she fills the "Step-mum" role. As she interacts with school and daycare along with myself and the kids mum, she often finds herself mistaken for the mother of my 3, and doesn't really know how to introduce herself and her relationship to the children.
Does anyone have any ideas for an alternative to Dad's Girlfriend or Step Mum?