I’ve been where you are now. When I met her, my late wife was anything but a natural domme. Didn’t have a dominant bone in her body, bless 'er, and hated the idea of causing me pain. I had to introduce her gradually to understanding that being dominated and made to endure ordeals was something I needed and found erotic.
We started very small: playful nipple tweaking, twisting and biting etc. To begin with, she’d flinch and stop doing a thing the instant I winced or let out a squeak, but by introducing a safeword system, I was able to “train” her to appreciate that for me, while pain is pain - it hurts as much as it does for anyone else! - I need to be required to endure it, and that she was to ignore any and all noises or pleas for mercy I might produce, as they were only to be expected.
It was a gradual process - took many months - and I made sure not to insist on BDSM content every time we had sex, but eventually she came not only to understand my needs but to enjoy our sessions. In short, she discovered the inner domme she never knew she had. She’d been raised to be a good, kind, sweet-natured person - and she remained this in daily life to the world at large - but with me, she found that our safe, consensual D/s dynamic enabled her to mine a rich seam of wickedness and playful cruelty she’d been taught to suppress, and she found it liberating.
Ours was definitely not one of those full-on 24/7 D/s relationships - hell, I didn’t go about in an iron collar and eat out of a dog bowl! - but even so, in time the playful roleplay thing seeped into daily life in a very pleasing way. Example: we’d be out shopping; I’d see a shirt I really fancied. Financially, I could have just taken it straight to the checkout, but where would have been the fun in that? Instead, I’d have to ask Mistress whether I might be “allowed” to have it. There would follow a pantomime of raised eyebrows, sharp intakes of breath and quizzical looks while she considered the question. She might even initially refuse, and make me beg her to change her mind. Eventually she would relent, but remind me that there’d be “a price to pay” for this indulgence …and then later, at home, I’d find out just how many strokes of the paddle/crop/cane a new shirt was worth. Happy days!
Anyway… enough of me getting nostalgic! As @Brufton and @Calie have said, talk with her (OUTSIDE the bedroom); discuss your needs, explain to her why it’s so important to you; above all, explain to her how domination can be a loving act that will strengthen the bond between you. Ask her if she has any fears/worries about it, and do your best to allay those fears. Unless she has some deep-rooted psychological aversion to behaving in a dominant way, together you’ll get there.