((NP))
Your curiosity when you were younger and now is totally normal. Your mom is a grownup and can have whatever feelings she needs to have about whatever you choose to share with her about this.

I have a couple friends who had relatives pop into their family tree in a similar way, and it was for both of them a positive experience, to meet these relatives. I'm not saying that will be like that for you (or even might be- you may choose not to pursue further), but there may be a different reaction than shameful secret...interest, excitement, curiosity.