Mother-in-law wants my infant baptized. Says it will seal in the holy spirit.

I'm an atheist, my wife is agnostic, and my Mother-in-law (who knows our stance on religion) wants my daughter baptized. When asked why, her response was originally that baptizing, "seals in the holy spirit." Hilarious!

After my wife and I talked about it, we decided that there is no harm in letting our child getting baptized. So we agreed to let her to take our kid to church and get wet.

Now that we've agreed to this whole water-on-head ritual, however, she's saying that baptism is also the time when we as parents commit to a lifestyle of raising our child with Christian values.

Has anyone else dealt with this scenario? I'd like some tips moving forward so I can keep my mother-in-law happy and keep my atheist arsenal at bay?

I'd love to open this conversation with my mother-in-law in to a full blown religious discussion... Are there any other rituals like baptisms that other religions like to apply to babies?

Can anyone confirm this idea that Christians believe that the holy spirit can be "sealed in?" AND if they do believe this, do they also have a timeline for when that slippery little devil can get out?