Can I ask what you wanted to achieve by telling her? Was it a fear of guilt if you started sneaking around or do you need her permission for things? You are grown up after all and should be able to make your own decisions. You have mentioned that she wants to make sure you are okay, does this mean seeing a doctor or something? If you provide a little more information on the conversation it may be helpful.
However I do want to help as I can see this is a situation hanging on a knife edge for you. There is a good Wikipedia article that explains the common misconception about diaper lovers and paedophiles. Maybe you could show her this, it is a trusted site for the most part.
This would at least be a start for her breaking down her objections, the rest will be up to you. We do not know your mother like you do, which means you are best placed to decide how to deal with this situation. I can imagine she is very confused right now, maybe hurt. She may be feeling like she has done something wrong as a parent. You need to really be honest with her, reassure her you are fine and this is just a quirky part of your personality. She will now be holding this 'secret' with you and you need to guide her as you are the expert. This is a big thing for a parent to deal with, the fact their child potentially has a fetish that could impact on their life very dramatically. You have a responsibility to take full control of the situation.
Apart from that I can only wish you luck and hope it all works out. And you can always come back to update us.
I have to say it's impressive you had the courage to talk to your mother. Generally I would advise against telling a parent as not much good comes out of it, I'm glad in your case she didn't freak out like most do. I don't really have much advice as I decided I would never tell my parents, but if it were me I wouldn't push my luck. I feel like if you start buying diapers and wearing and she catches you she might get upset and like you said assume your going to become a pedo. If it were me I would avoid buying diapers or at least avoid buying more than a few at a time and wait until you can live on your own. I think talking to her like an adult is good advice, but if your living with her remember it's her house and her rules and you don't have the right to disrespect them either.
MotherFaith directing you to that article in Wikipedia is a good move. I've read it several times as it helps me understand the why's of why are we attracted to diapers. Linked to the article is Love Mapping and you should read that as well.
I think you're sort of in a middle position where your mother isn't totally against it nor is she accepting. My mom, when she found out, sent me to see a psychiatrist at a residential mental facility. Your mom may decide to read the Wiki article or she may not, but if she does, she should realize that infantalism is not related to pedophilia other than they both fall under the broad umbrella of Paraphillias. Give her some time to accept all of this as the passage of time diminishes the shock value.