You can’t. 😳
Friends don’t have sexual or romantic feelings for each other, and if one of you does, it’s not a friendship any more. That’s for you to understand — not her. 😉 Sex changes relationships — but so, too, does simply having sexual feelings about someone. She may have been a ten year friend, but the relationship has now changed. Expect her to become jealous if you bring around a date or talk about someone you’re crushing on or interested in. Don’t expect her to give you honest answers when these situations arise, because she may be holding out hope that the two of you wind up together, and any thumbs up she’d give another woman you’re interested in, will sabotage her own chances with you.
I know it’s sad to lose a friend, but the reality is that most relationships do change, and you can still see her, but you have to see her differently now.