In the end, it's your decision. If your past has absolutely NO connection with who you are now, then conceal it. If you feel that she'll find out some other way and you want to be the one to tell her, then consider telling her. Either way, know that if you made sincere taubah to Allah SWT, you're not obligated to tell her your past.
Following are the hadiths that I mentioned earlier that I would share:
It was narrated that Abu Hurayrah said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: *“All of my ummah may be forgiven except those who commit sin openly. It is a kind of committing sin openly if a man does something at night, then morning comes and Allaah has concealed his sin, but he says, ‘O So and so, I did such and such last night,’ when his Lord has concealed him (his action) all night but in the morning he reveals that which Allaah had concealed for him.” *
Narrated by al-Bukhaari, 5721; Muslim, 2990
Abdullah Ibn Masoud (رضي الله عنه) related, ‘A man came to the Prophet and said: ‘O Messenger of Allah! I have mingled with a woman in the far side of al-Medina, and I fulfilled my desire short of actually having sexual intercourse with her. So, here am I, judge me according to what you decide.’ Umar Ibn al-Khattab (رضي الله عنه) then said: ‘Allah had kept your secret, why did not you keep your secret?’ [Sahih Muslim]
Messenger of Allaah (sallallahu `alayhi wa salam) said: “Refrain from these filthy matters (i.e. sins) that Allaah has forbidden, and if one of you is tried by committing any of them, then let him conceal them as Allaah has concealed them for him.” [Al-Haakim]
There are many Quranic verses also in this regard, but that would require mentioning the background of those verses and hence the post would become too lengthy.**
**
*Does your partner know that your ex’s e-mails still rest in your inbox’s secret folder? Or for that matter, does your partner know that you have an e-mail ID that’s very, very private? Or do you wish you had told him or her about that new pair of designer and frightfully expensive (of course!) sunglasses that you have stashed in your cupboard? It is said that honesty is the best policy, but do you think ‘absolute honesty’ is actually the best policy when it comes to relationships? Do you believe in sharing everything - every thought, every secret desire, every feeling - with your partner? Or do you think it’s not necessary to share everything; a few secrets after all, add that bit of spice to your relationship! *
Big no on sharing email or fb passwords. And i don't expect her to share with me either. Of course the exception is always there coz i wouldn't hide anything from her. I believe in full honesty. With that said..i do not think it's not necessary to share everything. For instance, if my wife wouldn't want to tell me anything about her brother or sister..something that she should only keep it to herself. I think she should. And vice versa of course here!
Better to bury/erase all the past evidences/things even those related to sentimental values of everything/everyone that shouldn't concern you or your present spouse in your present relationship/life.
No need to keep secrets but why share unnecessary information. Things that would only lead to creating misunderstandings/suspicions "waswasas" in your spouse's heart, why to make her life and your own difficult. Keep things simple and share everything that improves/strengthens your mutual relationship. Your present spouse has a right to know about what you do after your marriage with him/her. Rest would only come back to haunt you (and even her, if shared) if you didn't erase it from your mind/diary and heart/soul in order to move on in life.
These things, if not gotten over with (as soon as possible) would cause hindrance in your progress in life and in dealing with the challenges/tests that awaits you. (Better to strengthen your mutual bond before those tests hit you suddenly)