this is the mommy rarity that will be in my secondary next gen  
she is also from an AU i did a while ago that you can find here  
here is her basic story+her story in my universe B next gen
 
in this AU rainbowdash never completed her sonic rainboom as a kid which changed the fate of many ponies  
as for rarity she was led to a rock and felt mocked. she never got to feel the center of attention for the fabulous outfits she would make.  
insteed coco pommel was forced to step up and suck up her fear and find courage. coco rearranged the whole play and made it wonderful even with the simple outfits. the play was a success and coco found her talent as a planner of many traits.
 
rarity stayed away from everyone feeling down as she felt that there was nothing she could do, watching everyone she knew get their cutiemarks while she still didnt know her own. though she always found herself back to designing, but still not being able to figure out what dresses were missing. so she tried something easier, trains, airplanes and motorized carriages. she got her cutiemark for architecture for vehicles.  
she finally found pride in herself, feel like there was something she could pour her heart into and make look amazing.
 
in her later years she befriends applejack and twilight among many friends she had. applejack from the few jobs she had for the train company and then having bumped into twilight at the market in ponyville, were she also met her future husband, gizmo.  
she had treated him so kind and made him feel like he was worth something when she called him handsome and admired his robotic works.
 
he invited her to help him on projects at his job were he worked with flithy rich, who at the time was gizmo’s lover. for a while gizmo was so nervous to break up things with filthy rich as his bad side was nice at all and then the fact he might get rejected by rarity.  
but with the random encouragement from rarity he found the courage and did so.
 
now they are married with three successful daughters.