it depends how you look at it, she didn't have to tell you, shes been honest with you, but she wants you to know everything in her closet before you get serious, she trusts you enough to tell you, as you've said her kids don't even know. would you rather have not known?
have you told her everything from your 'past' ? i'm sure you would complain if you found out later, and you would say didn't she trust you enough to tell you, and but she has told you now and you complain
my misses told me she had a secret to tell me, took herdays to tell me, i thought she had killed someone the way she was going on, finally I got her to tell me..... she had a 10yr old son,, i said is that it.. and just
( i later found out if she didn't tell me, her sister or mom would have )
go easy on her, because if i was you i would thank her for her honesty.