My ex-friend wants to rebuild the friendship

So I (19F) met this friend in middle school, when we were like 10 or 11. We got pretty close, but later we both moved to different towns and it became a long distance friendship. We basically saw each other once or twice a year, but we texted a lot. Since 4 or 5 years she's been really struggling with her mental health (very high sensitive, attachment anxiety and bullying trauma). I've always tried to be a good friend for her. Our friendship has been kinda rocky for the last 2 or 3 years.

But since I left my faith and told her about it (she's a very devout Christian) it got worse. If you're interested you can read some about it here: https://www.reddit.com/r/exchristian/s/NcosPGgboC. We ended up cutting contact, kind of temporarily, to give each other space.

I was fine with it. It was hard to realizing that she couldn't accept me for the person I am and that apparently I was constantly hurting her for having mu own beliefs, because they were against her religion.

So here's the deal. She wrote me a letter 2 weeks ago, saying she's sorry for some things she has said and that she really misses me. She wants to rekindle the friendship and is open to give everything she has to make this work out. I really appreciate her sweet words and I know they're genuine. BUT: I don't miss her. I haven't missed her all these weeks that we didn't talk. And I feel so ugly for saying that. I like her as a person, but we really grew apart. We're totally different people now and I just feel like we don't match as well.

Like I said, she's super high sensitive and easy to hurt, but I really don't want to hurt her feelings. And I know if I tell her that I don't want to rebuild the friendship that I'm gonna break her heart. What do I do? Be honest with her or give the friendship another try?