I don't know but every time against this "champ" 
i always somehow lose , i don't know how is this possible ,but i just cant win against her. Even when ahead she always wins in the late game. Is it because i play 
or is she just TOOO god damn strong.
It's because you play into your hard counter.
Poppy's W can prevent you from from dashing (for mobility, damage or durability), Poppy can rush early defensive items (to let her survive your all-ins) and she can use her ultimate to disengage fights.
She is great at denying you the ability to snowball and for shutting you down during teamfights.
Poppy is really good as an anti-ganker. Most junglers have a problem ganking against her, and most champions have a problem laning against her. At the same time, she's not really good at bullying or pushing, herself, so you effectively have a very stable lane dynamic in most scenarios.
Poppy counter's riven pretty hard. Poppy is also a really good top laner over-all
