I have been friends with a girl for 20+ years. How do I tell her I want more w/out jeopardizing our friendship?

She was dating a good friend of mine when we met. I was also good friends with her dad till he ped away a few years ago R.I.P. Brother! She lived 200 miles away, and I would go with my friend and her dad all the time to see her & her mom, who I am also very close friends with. We were teenagers then & needless to say my friend and her have went their seperate ways. I have stayed in touch with thoughout the years either by phone e-mail or stopping in whenever we were close to the others town. We have never been together ually, it had never crossed my mind. (well maybe somewhat) About 4 months ago she got married. They moved to the city where I live and after about 2 months together she left him because he was very controlling and abusive. The night she left him he was arrested and went to jail for FVPA, the first person she called was me. I went and stayed with her for a few days, and help her move out of the house. Since then we have been spending alot of time together, I go see her or she comes to my house every day, and I am startin to have very strong feelings for her. I bought her a dozen roses a couple days ago and I enclosed a letter that basically said I was just trying to cheer her up, & take her mind off all the B.S. shes been goin through lately. It didnt reveal anything about my feelings for her. When she read the letter she told me "thats pretty sad that my piece of s#*t husband never bought me flowers, but MY BEST FRIEND Jim did"! That best friend thing made me feel great, but at the same time my heart sank! Its too soon after her divorce now but when the time comes, how do I tell her how I truly feel w/out ruining our friendship. I dont want to loose her as a friend, but I also think that I could make her happier than she has been in a long time. What the hell do I do, Im goin insane over this! I think abourt her every waking moment. PLEASE give me some advise, someone!!!