Daughter of my Heart - What is a step-moms role now?

My stbx has a daughter through a previous relationship.  Since the beginning (from age 3 to 11 for the daughter)she's been a huge part of our/my life...literally with us 1/2 the year if not more by way of regular weekly/weekend overnights and extra summertime stuff.  (Her mom lives in the same town and we are civil if not down right comfortable most of the time).

She's not just been a part of my life, but my parents and extended families life...my nephews were her cousins, my parents are grandma and grandpa...they take her to camp every summer, ect.

Stbx and I were the "doers" of our little co-parenting group.  Daughter always knew who to ask to sign up for this or that from gymnastics to soccer and swimming - we did it.  Most of the time, bio-mom and step-dad weren't around mainly because neither see the value in extracurricular activities, don't have the money and don't want to commit to the time it takes for this stuff. (I'm not judging, I just want you to get the full picture here).  And if it wasn't an activity for school or her...we were usually going somewhere - camping, local fairs, events..you get the point, our life with her was HUGE and I played a large role in that as does any woman 'managing' her household. (although in retrospect, stbx really should have headed this up.  hindsight is 20/20)

Step daughter and I always had a special relationship - she felt pretty comfortable talking to me about everything.  I'd hassle her about hygiene and etiquette, she'd repeatedly ignore me like every other kid in the world.  When her mom didn't want to take her bra shopping or buy her deodrant, I did.  (with persmission of course, we do try to play nice).  Part of my schedule was taking her to school every morning...I'd tickle her "Say it!, Say it" I'd torment until she'd giggle and say "Okay, I love you". 

Her mom is okay with me being in her life.  Dad has essentially abandoned her...she doesn't realize the first man to break her heart is her daddy...but when I asked he callously told me "do what you want with 'daughter' we don't make decisions together anymore'.  I think he said this because he knows he can't/won't provide and I will.  

He left it to me to break the news to her, and didn't see her for over 6 weeks, moved to a town 2 hours away and I doubt will do more than visit every other weekend.

And this is what worries me.  If mom and dad had it together, I'd feel way more comfortable bowing out.  But with daddy gone and mommy married to a moron who can't stand her kid and verbally abuses her, I just don't know what to do.  Can I stand aside and watch them break her spirit piece by piece?

I respect the hell out of any parent and know that I'm not hers, so  the logical side of me says to bow out gracefully and let her mom raise her in the manner she see fits -  And like I said, mom is okay with me seeing kiddo, but is this right?  Do I keep setting up playdates?(I've seen her at least once a week, and plan to see her Valentines Day and various other activities that were already planned with my family this year...she would be heartbroken to not be included now) 

It's clear when I see her she misses me and gives me a big hug, but the first question out of her mouth is "how is daddy"  It's crushing.  (not that I care that she asks about him, but it tells me he hasn't called her).  And I see that my visit is just a bandaid for daddy - I'm her only connection to what was of her childhood and that happy life she had with him (us).

I'm trying not to get too mushy here, but I stayed up all night weeping over this...I just don't know what's best for all involved here.  I'm not step-mom anymore...what do I do?  Should I stand fast and be there for her, softening the blow of losing her daddy, or simply say no longer my responsiblity and butt out.

For the first time since this whole debacle, I'm seriously confused and need some advice. Any experience or insight would be appreciated.