I’m so sorry to hear that you lost your mum at such a young age, and when your own daughter was so little. There is no set timeline on grief and delayed grief is definitely something that can happen. It can be particularly likely to happen when someone doesn’t have support or outlets for their feelings, or ends up ‘bottling up’ their feelings for some reason. It sounds as though you were understandably focused on parenting your own daughter, and perhaps you didn’t have the chance to fully grieve at the time.
It’s never too late to get some support, and I’m glad that you’ve taken the first step of writing things down here. There are many others here who have lost a parent and will understand some of what you are going through.
Here are some other posts about delayed grief that you might be interested to read:
And here are some other posts by users who have lost a parent at a similar age to you - feel free to post a reply to them if you would like to talk.