When you had the A, not only was it about what you did, but also about all the lies and deception. As a BS, I can tell you that you need complete transparency. No secrets at all, no matter what your intentions.
I do find it hard to take in that you hadn't realised this already. She's not going to trust you right now, how can she? She may be asking herself if it really was a gift for her...or for an OW. You may find that hard. But she cannot mind read, she cannot trust what you say and she only has your track record to go by right now.
If there is anything, anything at all that you have lied about, hidden or not wanted to remember, despite how rocky things seem, now is the time to tell her. Volunteering stuff (true stuff!) helps rebuild the trust. Her discovery of any secrets, shatters it.
I know because my WH is the king of TT, not just about the A, but other things he hid from me during most of our marriage. I wish that he could have really committed to R by complete transparency and honesty.
If there's no other hidden info from the A etc, then be open about how you feel (in fact, do this anyway). Tell her if you're having trouble getting over the OW, getting triggered etc. She probably won't like it,but the honesty will help to rebuild the trust in the long run.
Basically, allow yourself to be completely vulnerable to her, transparent, volunteer information don't wait to be asked, own your choices (no excuses or explanations because they sound like blame shifting to a BS) and say specific sorries.
I wish you well and hope you can both R